UC-NRLF 


ENGIN. 
LIBRARY 


B    3    112 


.  ricot 


Engineering 
Library 


THE 
ELECTRICAL  CONTRACTOR 


McGraw-Hill  BookCompany 


Electrical  World         The  Engineering  and  Mining  Journal 
Engineering  Record  Engineering  News 

Railway  Age  Gazette  American  Machinist 

Signal  Engineer  American  Engneer 

Electric  Railway  Journal  Coal  Age 

Metallurgical  and  Chemical  Engineering  P  o  we  r 


THE  ELECTEICAL 
CONTRACTOR 


PRINCIPLES  OF  COST-KEEPING  AND   ESTIMATING, 

WIRING  AND.  ILLUMINATION  CALCULATIONS 

AND  OTHER  TECHNICAL  PROBLEMS 

OF  THE  BUSINESS 


BY 
LOUIS  W.  MOXEY,  JR. 

VICE-PRESIDENT,    KELLER-PIKE   CO. 
PHILADELPHIA,    PA. 


FIRST  EDITION 


McGRAW-HILL  BOOK  COMPANY,  INC. 

239  WEST  39TH  STREET,  NEW  YORK 

6]AND  8]BOUVERIE  STREET,  LONDON,  E.  C. 

1916 


/A 


Engineering 
Library 


COPYRIGHT,  1916,  BY  THE 
McGRAW-HiLL  BOOK  COMPANY,  INC. 


/iu:  c  A  <x 


THK    MAI'LK     I'KKSS    YORK    PA 


PREFACE 

Only  a  few  years  ago  the  electrical  contractor  was  an 
individual  mechanic.  The  period  of  evolution  to  the 
organized  business  of  today  has  been  too  short  to  permit 
of  much  standardization  in  systems  of  methods  of  han- 
dling work,  and  many  men  are  suffering  today  the  costly 
consequences.  The  need  of  better  methods  in  both  the 
commercial  and  technical  phases  is  evident  to  anyone 
who  comes  in  contact  with  the  average  contractor's 
organization  and  work. 

In  the  hope  that  the  essentials  of  the  writer's  system, 
developed  during  the  past  twenty  years,  and  the  tech- 
nical data  accumulated  in  connection  therewith,  may  be 
of  assistance  to  other  contractors,  the  author  has  ven- 
tured to  publish  this  material  in  book  form.  Much  of 
the  material  has  already  appeared  in  the  Electrical  World. 

L.  W.  M.,  JR. 

PHILADELPHIA,  PA, 
February,  1916. 


338063 


CONTENTS 

PAGE 

PREFACE   v 

CHAPTER 

I.     Profit  and  Overhead  Expense 1-6 

II.     Bookkeeping 7-13 

III.  Cost-keeping 14-40 

IV.  Estimating 41-45 

V.     Calculating  Wire  Sizes  for  D.  C.  Currents 46-52 

VI.     Calculating  Wire  Sizes  for  A.  C.  Currents 53-61 

VII.     Illumination  Calculations 62-73 

VIII.     General  Data 74-80 

INDEX  81 


vn 


THE 
ELECTRICAL  CONTRACTOR 

CHAPTER  I 
PROFITS  AND  OVERHEAD  EXPENSE 

PROFITS 

The  two  primary  requisites  for  achieving  success  in 
the  conduct  of  an  electrical-contracting  business  are 
a  knowledge  of  business  principles  and  methods  and  a 
knowledge  of  electrical  construction  and  the  related 
engineering  problems.  Each  of  these  factors  is  of  equal 
importance,  and  real  success  in  the  electrical-contract- 
ing business  cannot  be  obtained  if  either  of  these  two 
factors  be  lacking. 

Of  primary  importance  to  every  contractor  and  every 
business  man  is  the  subject  of  profits.  Every  man  in 
business  desires  to  make  a  profit,  but  many  have  only  a 
vague  idea  of  the  meaning  of  the  word.  To  illustrate 
what  is  meant  by  the  word  " profit"  take  the  case  of  a 
corporation.  It  has  not  made  a  profit  on  its  year's 
business  unless  the  amount  of  money  received  or  assur- 
able  of  collection  without  cost  within  a  reasonable  length 
of  time  exceeds  the  amount  of  money  expended  during 
the  year.  The  amount  of  money  expended  by  a  cor- 
poration doing,  for  example,  an  electrical-contracting 
business  includes  not  only  the  amount  paid  for  labor 
and  material  actually  used  on  its  jobs  but  all  amounts 

l 


2  THE  ELECTRICAL  CONTRACTOR 

paid  for  labor  and  material  whether  chargeable  to  any 
particular  job  or  not.  In  other  words,  the  material 
item  should  embrace  the  cost  of  engines  and  dynamos  as 
well  as  ink  and  pencils,  and  the  labor  item  should  include 
not  only  the  pay  of  the  journeymen  and  helpers  but  also 
the  salaries  of  the  president  and  other  officers. 

If  a  corporation  makes  a  profit  on  its  year's  business 
only  under  the  conditions  outlined,  an  individual  or  a 
group  of  individuals  can  make  a  profit  only  under  the 
same  conditions.  The  error  which  many  persons  who 
do  a  small  business  make  is  that  they  fail  to  include  in 
the  amount  of  money  expended  for  labor  during  the  year 
a  salary  for  themselves.  This  should  be  equal  to  the 
sum  that  they  would  have  to  pay  a  person  or  persons 
for  doing  their  work  and  producing  the  same  results. 
Hence  many  persons  doing  a  small  business  and  neglect- 
ing to  include  a  salary  for  themselves  in  the  labor  item 
do  not  make  a  profit.  What  appears  to  be  profit  may 
merely  be  a  salary — perhaps  meager  at  that. 

OVERHEAD  EXPENSE 

There  are  two  items  which  combined  compose  the 
cost  of  conducting  an  electrical-contracting  business. 
These  must  be  taken  into  consideration  when  figuring 
profits.  The  first  item  includes  the  cost  of  materials 
and  labor  actually  used  on  jobs,  such  as  engines,  dy- 
namos, panelboards,  conduit,  wire,  etc.,  together  with 
the  salaries  of  the  foreman,  journeymen,  helpers  and 
apprentices.  This  item  may  be  called,  for  convenience, 
shop  or  raw  cost. 

The  second  item  includes  the  cost  of  materials  and 
labor  expended  in  securing  a  contract  and  in  the  exe- 
cution of  the  job.  It  embraces  the  salaries  of  the  officers, 


PROFITS  AND  OVERHEAD  EXPENSE  3 

bookkeeper,  stenographer,  bill  clerk,  draftsman,  super- 
intendent, etc.,  and  the  cost  of  rent,  heat,  light,  taxes, 
insurance,  stationery,  postage,  telephone  and  the  like. 
This  item  is  called  manufacturer's  expense  or  overhead 
charge.  The  shop  or  raw  cost  is  always  more  or  less 
an  uncertain  one  and  will  be  dwelt  upon  in  detail  in 
Chap.  Ill,  while  overhead  charges  can  be  fairly  well 
determined. 

From  a  collection  of  data  compiled  by  the  National 
Electrical  Contractors'  Association  on  the  costs  of  con- 
ducting an  electrical-contracting  business,  it  appears 
that  the  overhead  expense  of  an  electrical  contractor 
lies  between  about  15  and  25  per  cent,  of  his  shop  cost 
and  that  the  average  profit  is  figured  at  from  5  to  15 
per  cent,  of  the  gross  cost,  depending  upon  the  terms  of 
the  contract  and  the  nature  of  the  work. 

The  following  outline  gives  a  list  of  items  which  enter 
into  a  contractor's  overhead  expense: 

Officers'  salaries. 
Salaries  of  office  employees. 
Salary  of  superintendent. 

Estimating  and  selling  expense  (car  fare,  railroad  fare,  entertaining, 
etc.). 

Stationery  and  sundries. 

Postage,  telephone,  telegrams. 

Depreciation  of  tools  and  furniture. 

Insurance  on  property,  furniture,  stock,  etc. 

Liability  and  compensation  insurance  (if  any). 

Interest  on  investment. 

Rent  (if  owner  of  building,  taxes  and  depreciation). 

Heat  and  light. 

Repairs. 

Attorneys'  fees. 

License  fees  (if  any). 

Association  dues. 

Miscellaneous. 


4  THE  ELECTRICAL  CONTRACTOR 

This  list  may  be  said  to  include  the  items  which  almost 
every  electrical  contractor  must  include  in  figuring  his 
overhead  expense,  but  not  necessarily  all  the  items  which 
he  must  include.  Most  contractors  find  it  necessary  to 
employ  one  or  more  automobiles  in  their  business.  If 
such  is  the  case,  the  interest  on  the  investment  made  for 
automobiles,  the  depreciation  of  the  machines,  the  cost 
of  garaging,  the  cost  of  operating  and  the  cost  of  upkeep 
must  be  included  in  the  overhead  expense.  Some  con- 
tractors have  other  expenses,  such  as  advertising,  etc., 
that  are  properly  considered  as  items  in  overhead  ex- 
pense. Hence,  the  list  given  is  not  complete  but  merely 
suggestive  of  the  items  which  enter  into  a  contractor's 
overhead  expense. 

METHOD  OF  COMPUTING  AND  APPLYING  OVERHEAD  EXPENSE 
AND  PROFIT 

From  the  preceding  paragraphs  it  can  readily  be  seen 
that  any  estimate  for  work  which  does  not  include,  in 
addition  to  an  estimate  of  shop  cost,  an  item  for  manu- 
facturer's expense  is  one  that  will  result  in  a  loss  to  the 
contractor. 

The  writer  has  found  it  more  convenient  and  logical 
to  compute  the  manufacturer's  or  overhead  expense  as  a 
percentage  of  the  shop  cost,  instead  of  as  a  percentage 
of  the  selling  price.  An  estimate  of  overhead  expense 
should  be  made  at  least  once  or  twice  a  year  and  the  per- 
centage thus  obtained  added  to  the  shop  cost  in  all  esti- 
mates made  in  the  succeeding  period  to  obtain  the  real 
cost.  For  example: 

Shop  cost: 

Pay  of  foremen,    journeymen,    helpers   and    apprentices    $80,000.00 

Cost  of  material,  engines,  generators,  conduit,  wire,  etc.  .     200,000.00 

Total  shop  cost $280,000. 00 


PROFITS  AND  OVERHEAD  EXPENSE  5 

Overhead  expense: 

Salaries  of  employers,  co-partners  or  officers $30,000.00 

Salaries  of  office  employees — bookkeepers,  clerks,  etc 8,000.00 

Salaries  of  superintendent,  draftsman  and  engineer 10,000.00 

Stationery,  telephones,  taxes,  insurance,  rent,  etc 8,000 . 00 


Total  manufacturer's  expense $56,000.00 

Manufacturer's  or  overhead  expense  as  a  percentage  of  shop  cost  equals 
$56,000  -T-  $280,000,  or  20  per  cent. 

The  real  cost,  therefore,  of  the  year's  business  would 
be  the  shop  cost,  $280,000,  plus  the  overhead  expense 
of  $56,000,  or  $336,000.  Should  the  selling  value  of  this 
work  be  $369,600,  the  contractor  has  made  a  profit  of 
10  per  cent,  on  the  investment  made.  Should  the  selling 
value,  however,  be  only  $334,992,  he  has  lost  3  per  cent, 
on  his  investment.  A  true  estimate  should,  therefore, 
be  made  for  any  job  as  follows: 

Shop  cost $10,000.00 

Overhead  expense  at  20  per  cent 2,000. 00 


Real  cost $12,000.00 

Profit  at  10  per  cent 1,200 . 00 


Amount  of  proposal. $13,200.00 

Some  contractors  figure  their  overhead  expense  as  a 
percentage  of  the  selling  price.  If  a  contracotr's  over- 
head expense  is  20  per  cent,  of  his  selling  price  and  he 
desires  to  make  a  profit  of  10  per  cent,  on  the  selling 
price,  he  would  not  make  it  if  he  used  the  following 
method: 

Shop  cost $1,500.00 

20  per  cent,  overhead  expense  plus  10  per  cent,  profit 450 . 00 


Amount  of  proposal $1,950 . 00 

To  get  the  results  desired — namely,  20  per  cent,  of 
selling  price  as  overhead  expense  and  10  per  cent,  of 


6  THE  ELECTRICAL  CONTRACTOR 

selling  price  as  net  profit — the  estimate  should  be  made 
in  the  following  manner:  If  the  shop  cost  is  $1,500, 
this  amount  must  represent  70  per  cent,  of  the  selling 
price,  for  the  overhead  expense  is  taken  as  20  per  cent, 
of  the  selling  price  and  the  profit  is  taken  as  10  per  cent, 
of  the  selling  price.  Hence  the  selling  price  should  be 
($1,500  -r-  70)  X  100,  or  $2,142.  The  overhead  expense 
is  20  per  cent,  of  $2,142,  or  $428,  and  the  profit  is  10  per 
cent,  of  $2,142,  or  $214.  The  sum  of  these  two  items, 
$642,  subtracted  from  the  selling  price  leaves  the  origi- 
nal shop  cost  of  $1,500.  Hence  the  previous  method 
of  estimating  was  in  error  by  $2,142  -  $1,950,  or  $192, 
as  shown. 

But  the  entire  principle  of  applying  overhead  expense 
and  profit  as  percentages  of  the  selling  price  is  wrong. 
Profit  on  a  job  is  actually  interest  on  an  investment. 
The  investment  in  the  contractor's  business  is  the  sum 
of  the  shop  cost  and  the  overhead  expense.  Hence  the 
profit  should  be  computed  as  a  percentage  of  this  sum. 


CHAPTER  II 
BOOKKEEPING 

Different  systems  of  bookkeeping  are,  of  course,  in 
use  by  electrical  contractors.  Some  lack  merit  and 
others  are  of  great  usefulness.  In  designing  any  book- 
keeping system  it  should  be  borne  in  mind  that  the 
simpler  the  system  can  be  made  the  more  satisfactory 
and  efficient  it  will  prove  to  be,  provided  that  it  gives 
all  the  information  that  the  contractor  should  have 
about  his  business,  such  as  overhead  expense,  cost  of 
labor  and  materials  for  each  individual  piece  of  work 
and  the  gross  profit  of  the  same. 

The  system  of  bookkeeping  to  be  described  is  the  one 
employed  by  the  firm  with  which  the  writer  is  connected. 
This  system  has  been  found  very  satisfactory  and 
requires  the  minimum  of  labor. 

Upon  the  receipt  of  an  order  for  performing  a  certain 
piece  of  work,  an  order  card  (Fig.  1)  is  filled  out  and 
turned  over  to  the  credit  department,  where  the  rating, 
financial  responsibility,  etc.,  of  the  prospective  customer 
is  examined.  If  the  result  of  this  inquiry  is  satisfactory, 
the  card  is  passed  to  the  bookkeeping  department, 
where  the  information  contained  on  the  card  is  entered 
in  the  contract  ledger  and  the  card  filed  in  the  order- 
card  index  file. 

In  the  contract  ledger,  under  the  entry  for  the  job,  are 
charged  all  labor  and  material  actually  used  on  the  job 
until  the  work  is  completed,  no  entry  being  made,  how- 
ever, for  office  expense. 

7 


ELECTRICAL  CONTRACTOR 


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BOOKKEEPING  9 

After  the  plans  and  specifications  for  the  work  are 
received  the  engineering  department  lays  out  the  work, 
straightens  out  any  discrepancies  between  the  plans  and 
the  specifications,  and  secures  any  other  information 
which  may  be  necessary  for  the  construction  depart- 
ment to  know  before  proceeding  with  the  actual  work. 
The  plans  and  specifications  are  then  turned  over  to  the 
construction  department,  the  superintendent  of  which 
fills  out  a  job  card  (Fig.  1)  with  the  name  of  the  man 
who  has  been  selected  to  be  foreman  of  the  work.  The 
card  then  becomes  the  foreman's  order  for  the  work 
and  is  kept  by  him  until  the  completion  of  the  job. 
When  the  card  is  returned,  the  bookkeeping  department 
knows  the  job  has  been  completed  and  is  ready  for 
billing.  This  process  is  repeated  in  the  case  of  any  ex- 
tra work  which  may  be  ordered  by  the  customer,  no 
foreman  or  workman  being  permitted  to  do  any  extra 
work  on  a  contract  until  a  job  card  for  the  same  has 
been  issued. 

When  the  construction  department  starts  a  piece  of 
work  the  superintendent  fills  out  a  stock-requisition 
sheet  (Fig.  2).  To  guide  him  in  ordering  materials  a 
copy  of  the  estimate  showing  the  estimated  amounts  of 
materials  needed  is  also  given  him.  Upon  the  receipt 
of  the  material  at  the  job  a  second  list  is  filled  out  on  a 
special  receipt  form  and  receipted  by  the  man  in  charge. 
After  a  job  is  completed,  the  surplus  material  is  again 
listed  and  returned  to  the  stock  room,  where  the  stock 
clerk  enters  the  amount  of  material  received  on  another 
special  receipt  form.  Sheets  such  as  those  described  are 
also  filled  out  by  the  foreman  in  charge  when  material 
is  transferred  from  one  job  to  another  and  does  not  pass 
through  the  stock  room. 


10 


THE  ELECTRICAL  CONTRACTOR 


0 

Note:  -No  material  will  be  given 
Separate  sheets  must  be  n 
taken  that  no  writing  or  it 

Materials  can  not  always  be 
but  must  be  purchased.  Thereto 
much  ahead  as  possible  of  the  d 
actually  needed.    In  urgent  case 
available  make  requisition  by  ph 
written  sheet  to  confirm  it.  Try 
requisitions  in  at  least  as  early 
ials  are  needed.  Stockroom  is  o 

No.                              JOB  NAME 

OPAl 

STOCK-REQUISITION  SHEET     Week  Ending 

without  a  requisition  neatly  and  completely  filled  out. 
lade  out  for  each  job  or  extra,  and  in  making  out  requisitio 
larks  be  made  in  right  hand  column. 

sent  from  our  stockroom, 
re  make  requisitions  as 
ate  when  materials  are 
8  whern  K  telephone  ia            r»pt«                                       n«t*  W™ 

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KELLER-PIKE  CO. 

KELLER-PIKE  CO.Gentlemen:-Please  send  the  following  material  for  use  on  job  of  which  I  have  c 

Ordered 

Amoun' 
Filled 
From 

Supply 

Amount 
Filled 
From 
Stock 

Amount 
Wanted 

DESCRIPTION  OP                               Amount 

/alue  from  Stock 

Order  No 

ARTICLES  WANTED                         Brought  Fwd. 

FIG.  2. — Requisition  sheet  for  construction  materials. 


BOOKKEEPING  11 

By  referring  to  the  stock-requisition  sheet  (Fig.  2), 
it  will  be  noticed  that  the  amount  of  material  desired  is 
placed  in  the  fourth  column  from  the  left,  the  amount 
of  that  material  supplied  from  the  stock  room  in  the 
next  column,  and  in  the  adjoining  two  columns  the 
amount  of  that  material  furnished  by  any  local  supply 
house,  together  with  the  initials  of  the  supply  house 
and  the  contractor's  order  number  to  the  supply  house. 
All  material  going  to  a  job  is,  therefore,  entered,  but 
only  that  portion  of  the  materials  supplied  from  the 
stock  room  is  valued  on  the  sheet,  the  amount  being 
credited  to  the  stock  room  and  charged  to  the  job.  The 
material  furnished  by  the  supply  house  is  billed  by  the 
supply  house,  whose  account  in  the  main  ledger  is  cred- 
ited and  the  amount  charged  in  the  contract  ledger. 
The  list  of  materials  on  the  requisition  sheets  becomes, 
therefore,  the  bookkeeping  department's  "  sheet  of  origi- 
nal entry,"  and  these  sheets  are  filed  in  an  indexed  loose- 
leaf  ledger.  The  other  material  sheets  mentioned  are, 
on  the  other  hand,  simple  memoranda  for  checking  and 
receipts  for  materials. 

To  charge  the  stock  room  and  credit  a  job  on  the 
return  of  materials,  or  to  credit  one  job  and  charge 
another  where  materials  have  been  transferred  without 
passing  through  the  stock  room,  a  sheet  similar  to  the 
requisition  form,  but  of  different  color,  is  filled  out  in 
the  office  from  the  data  contained  on  the  other  types  of 
material  sheets  mentioned. 

The  bills  for  work  done  can  be  made  out  readily,  the 
price  being  already  established.  In  time-and-material 
work  it  is  necessary  for  the  billing  clerk  to  refer  to  his 
contract  ledger  and  copy  down  all  material  and  labor 
items  which  have  been  charged  to  the  work,  giving  the 


12  THE  ELECTRICAL  CONTRACTOR 


DISTRIBtlTIO'N  OF  PAYROLL  —  WEEK  Els 

rnrvn                                19 

NAME  OF  JOB 

LABOR 

EXTRAS 

TOTAL 

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LJ 

TOTAL 

FIG.  3. — Form  of  payroll  (itemized). 


BOOKKEEPING  13 

price  at  which  the  same  were  charged  and  noting  whether 
the  material  was  furnished  from  the  stock  room  or  from 
a  supply  house.  This  bill  is  made  out  in  pencil  and 
turned  over  to  the  construction  department,  by  which 
it  is  examined  and,  if  found  correct,  passed  to  the  person 
pricing  the  material  and  labor. 

The  distribution  of  the  labor  on  various  jobs  is  made 
by  the  pay-roll  clerk  on  a  pay-roll  sheet  (Fig.  3),  and 
the  various  jobs  are  charged  and  the  cash  account  cred- 
ited from  this  sheet. 


CHAPTER  III 
COST-KEEPING 

In  order  to  obtain  figures  on  costs  it  is  necessary  for  a 
contractor  to  employ  such  cost-keeping  systems  as  will 
enable  him  to  know  the  unit  costs  of  performing  the 
various  operations  entering  into  the  execution  of  any 
wiring  contract.  Unless  a  contractor  does  employ  such 
cost-keeping  methods,  he  can  hardly  be  said  to  be  en- 
gaged in  business,  for  he  is  merely  playing  a  game  of 
chance  with  his  entire  investment  and  business  future 
at  stake. 

In  estimates  for  work  there  are  two  items  of  costs : 

1.  Costs  of  material. 

2.  Costs  of  labor. 

No  accurate  figures  for  use  in  estimating  the  cost  of 
the  materials  used  on  a  job  can  be  given,  owing  to  the 
constant  changes  in  price  of  most  of  these  materials, 
such  as  wire,  conduit,  etc.  On  the  other  hand,  while 
the  rates  paid  for  labor  change,  the  changes  are  not  of 
frequent  occurrence  and  tables  of  labor  costs  can  be 
worked  out  on  the  present  rates  for  labor  and  any  in- 
crease or  decrease  of  rates  can  be  taken-  care  of  by 
employing  a  percentage  correction  factor. 

For  engines,  generators,  motors,  transformers,  etc., 
it  is  always  best  to  secure  a  bid  on  the  apparatus  direct 
from  the  manufacturer,  especially  if  a  reasonable  time 
be  given  the  contractor  to  prepare  his  estimate.  It  is 
preferable  to  have  these  quotations  include  the  cost  of 

14 


COST-KEEPING  15 

the  apparatus  delivered  and  erected  in  position,  as  well 
as  the  cost  of  foundations,  templets,  bolts,  painting, 
etc.  There  are  two  reasons  for  this  procedure:  First, 
unless  the  percentage  of  profit  is  large,  the  contractor 
should  not  undertake  the  risk  of  accepting  the  apparatus 
f.o.b.  point  of  delivery  and  taking  the  responsibility 
for  any  damage  that  may  occur  to  the  same  before  it 
is  accepted  by  the  owner.  Second,  the  contractor  is 
very  likely  to  omit  a  number  of  items  in  estimating  on 
such  apparatus,  and  these  items  combined  may  amount 
to  a  considerable  sum  even  though  each  is  small  itself, 

Should,  however,  the  job  be  a  large  one  and  the  time 
for  preparing  an  estimate  be  short,  the  approximate 
cost  of  the  apparatus  could  be  determined  if  the  con- 
tractor has  prepared  curves  of  cost  for  the  various 
sizes  of  such  apparatus  in  the  past  and  had  frequently 
checked  them.  Such  checking  is  absolutely  necessary, 
as  apparatus  may  vary  considerably  in  price  within 
comparatively  short  periods  of  time.  Fig.  4  shows  how 
these  curves  should  be  prepared. 

Separate  curves  or  tables  should  be  prepared  for 
directly  connected  and  belted,  single  and  four-valve  or 
Corliss  engines,  also  for  directly  connected  and  belted, 
direct-current  and  alternating-current  generators  of 
various  types,  as  well  as  for  motors  of  low,  medium  and 
high  speeds,  etc. 

The  same  method  could  be  followed  for  figuring  the 
cost  of  certain  other  kinds  of  materials,  although  greater 
accuracy  must  be  used  in  plotting  some  curves,  for  in 
some  cases  price  differences  of  a  few  cents  may  be  de- 
sired. This  method  is  not  intended  to  be  pushed  to 
its  logical  conclusion  and  made  to  apply  to  such  items 
as  switches,  outlet  boxes,  receptacles  and  the  like,  the 


16 


THE  ELECTRICAL  CONTRACTOR 


4»UU 

4600 
4400 
4200 
4000 
3800 
3600 
3400 
3200 
3000 
2800 
2600 
2400 
2200 
2000 
1800 
1600 
1400 
1200 
1000 
800 
600 

/ 

/ 

/ 

. 

7 

/ 

/ 

/ 

*,/ 

/ 

t^1/ 

y 

/ 

y" 

<: 

/ 

.p* 

*"/ 

/ 

f 

^ 

r 

y 

h 

^< 

^ 

/ 

^ 

/ 

/' 

s 

~? 

/ 

if  x 

X 

/ 

y 

/  x 

/ 

/ 

'  / 

x 

/ 

V/ 

/ 

'/ 

, 

^ 

)  20  40  60  80  100  120  140  160  180  200  220  240  260  280  300  320  340  360  380  40 

Sizes  of  Generators  in  K.V.A. 

FIG.  4. — Curves  showing  the  cost  of  directly  connected  engine-driven 
direct-current  and  alternating-current  generators  installed  under  ordi- 
nary conditions,  the  bases  being  furnished  by  engine  contractor. 


COST-KEEPING  17 

prices  of  which  the  contractor  generally  has  at  his  finger 
tips,  but  it  can  be  applied  advantageously  to  such  mate- 
rial as  panel  boxes,  panelboards,  doors  and  trim,  an- 
nunciators, watchmen's  clocks,  etc. 

For  checking  purposes  or  naming  approximate  costs 
to  an  owner  for  work  being  done  on  a  time-and-material 
basis,  this  method  can  be  used  with  the  labor  and  material 
costs,  combined  as  the  data  for  these  costs  can  be  secured 
in  the  contract  ledger  from  the  completed  jobs. 

Take  the  following  example,  which  is  the  cost  for 
wiring  a  new  residence  of  brick-and-joist  construction 
b*y  the  concealed-conduit  method.  The  service  cables 
were  run  down  the  outside  wall,  the  meter  being  in- 
stalled in  the  basement.  The  system  was  three-wire, 
110-220-volt,  single-phase.  The  panelboards  were  of 
slate  with  30-amp.  type  B  switches,  mounted  in  iron 
boxes,  with  wooden  doors  and  trim.  The  switches  were 
of  Cutter  manufacture  and  the  receptacle  of  the  flush 
wall  type  and  of  Pringle  manufacture.  The  wire  was 
rubber-covered  and  of  the  National  Electrical  Code 
standard. 

The  shop  cost  as  shown  by  the  contract  ledger  was 
$400.75,  the  cost  items  being  as  follows: 

Materials $254 . 36 

Labor 136 . 74 

Car  fare,  etc 9 . 65 


Shop  cost $400.75 

The  residence  had  32  light  outlets,  28  switch  outlets 
and  20  receptacle  outlets.  The  cost  of  a  switch  plus 
the  labor  of  installing  it  was  $1  and  the  cost  of  a  recep- 
tacle plus  the  labor  of  installing  it  was  $1.10. 

If  all  outlets  were  light  outlets,  the  shop  cost  would 


18 


THE  ELECTRICAL  CONTRACTOR 


have  been  approximately  $400.75  -  [(28  X  $1)  +  (20 
X  $1.10)]  or  $350.75.  Dividing  $350.75  by  the  total 
number  of  outlets,  which  is  80,  $4.38  is  obtained.  Hence 
$4.38  is  the  cost  of  wiring  per  light  outlet.  The  cost  of 
wiring  a  switch  outlet  is  $4.38  +  $1,  or  $5.38,  and  the 
cost  of  wiring  a  receptacle  outlet  is  $4.38  -f  $1.10,  or 
$5.48. 

This  method  is  fairly  accurate  for  small-residence 
work,  and  any  number  of  costs  per  outlet  may  be  com- 
piled to  cover  the  various  types  of  wiring  construction, 
wiring  systems,  etc. 

Tables  I  to  XI,1  inclusive,  give  data  from  which  such 
curves  can  be  plotted,  or,  if  desired,  the  data  may  be 
retained  in  tabular  form.  Too  much  emphasis,  however, 
cannot  be  laid  on  the  advisability  of  preparing  such  tables 
and  curves  from  one's  own  records. 

1  Figures  in  Tables  I,  II,  III  and  V  are  the  figures  the  electrical  con- 
tractor would  secure  from  his  subcontractors.  Tables  IV,  VI,  VII,  VIII, 
IX,  X  and  XI  include  the  contractor's  overhead  expense  and  profit. 


TABLE    I. — COST    OF    ENGINES    AND    THEIR    FOUNDATIONS    INSTALLED 
READY  FOR  STEAM-PIPE  CONNECTIONS1 


Horsepower  rating 

Single 

Tandem-compound 

Four-valve 

50-100 
100-200 
300  and  above 

$16.00 
15.00 
14.00 

$26  .  00 
24.00 

$25.00 
23.00 

1  Installed  ready  for  steam-pipe  connections  under  ordinary  condi- 
tions. The  figures  given  are  based  on  data  from  the  Ames  Iron  Works, 
Oswego,  N.  Y. 


COST-KEEPING 


19 


TABLE    II. — COST    OF    DIRECTLY    CONNECTED    DIRECT-CURRENT    AND 
ALTERNATING-CURRENT  GENERATORS1 


Direct-current 

Alternating-current 

Rating,  kw.                   Cost  per  kw. 

Rating,  kva. 

Cost  per  kva. 

25 

$25.00 

50 

$16.00 

35 

23.00 

75 

14.00 

50 

20.00 

125 

13.00 

75 

16.00 

135 

12.00 

100 

15.00 

185 

10.00 

125 

14.00 

250 

9.00 

150 

13.00 

312 

9.00 

200 

12.00 

350 

8.00 

250 

12.00 

375  and  above 

8.00 

300  and  above 

12.00 

1  These  prices  are  based  on  engine-driven  generators  installed  under 
ordinary  conditions,  the  sub-bases  for  the  erection  of  the  generators  being 
furnished  by  the  engine  contractor.  The  values  given  are  based  on  data 
obtained  from  the  General  Electric  Company. 


TABLE  111. — COST  OF  SWITCHBOARDS,  INCLUDING  DYNAMO  AND  FEEDER 
PANELS,  220  VOLTS  OR  LESS1 


Direct-current 


Alternating-current 


Rating,  kw. 

Cost  per  kw. 

Rating,  kva. 

Cost  per  kva. 

25-   50 
50-100 
100  and  above 

$5.00-$10.00 
4.00-  8.00 
3.00-  6.00 

50-125 
125-350 
350  and  above 

$4.00-$6.00 
3.00-  4.00 
2.00-  3.00 

1  The  range  of  prices  is  due  to  variations  in  the  grade  of  materials  and 
workmanship,  the  number  of  instruments,  switches,  etc.  These  figures 
include  the  switchboards  erected  complete  and  ready  for  the  connection 
of  generator  cables,  power  and  light  feeders,  etc.  The  prices  are  based  on 
data  obtained  from  the  Walker  Electric  Company,  Philadelphia. 


20 


THE  ELECTRICAL  CONTRACTOR 


TABLE  IV. — COST  OF  DYNAMO  CONNECTIONS' 


Direct-current 

Alternating-current 

Rating, 
kw. 

Lead-sheathed 
rubber 
insulation 

Rubber-covered 
cable  in 
conduit 

Rating, 
kva. 

Lead-sheathed 
rubber 
insulation 

Rubber-covered 
cable  in 
conduit 

25-  50 
50-100 
100  and 
above 

$50.00-$  150.  00 
75.00-  250.00 
100.00-  350.00 

$25.00-$125.00 
50.00-  225.00 
75.00-  325.00 

50-125 
125-350 
350  and 
above 

$100.00-$300.00 
200.00-  400.00 
300.00-  500.00 

$75.00-8275.00 
175.00-  375.00 
275.00-  475.00 

1  The  average  flat  distance  between  dynamo  and  switchboard  has 
been  assumed  as  25  ft. 


TABLE  V. — COSTS  PER  HORSEPOWER  OF  MOTORS  AND  NECESSARY  RHEO- 
STATS AND  CONTROLLERS  ERECTED1 


Direct-current 


Alternating-current 


Horsepower 

Cost 

Horsepower 

Cost 

1           3 

$50  .  00 

1    -  IH 

$60.00 

5     -  7H 

40.00 

IK-  2 

50.00 

7K-  10 

30.00 

2-3 

40.00 

10     -  15 

25.00 

3     -  7H 

30.00 

15     -  25 

20.00 

7^-10 

25.00 

25     -  50 

18.00 

10     -20 

20.00 

50     -100 

15.00 

20     -35 

18.00 

100    -250 

13.00 

35     -75 

15.00 

250  and  above 

12.00 

100  and  above 

13.00 

1  Motors  are  assumed  to  be  of  standard  speeds,  voltage,  etc.,  and  to  be 
erected  on  floor,  cost  of  foundations  not  being  included.  The  costs 
include  delivery  and  erection  ready  for  wiring  connections  and  are  based 
on  data  obtained  from  the  General  Electric  Company. 


COST-KEEPING 


21 


TABLE  VI. — COSTS  OF  WIRING  AND  CONNECTING  MOTORS,  INCLUDING 
ALL  LABOR  AND  MATERIALS1 


Horsepower 

Porcelain 

Molding 

Conduit 

1-  5 

$7  .  50-$75  .  00 

$10.00-$100.00 

$15.00-1150.00 

5-10 

30.00-120.00 

40.00-  170.00 

60.00-  240.00 

15-25 

75.00-250.00 

90.00-  300.00 

150.00-  300.00 

25-50 

100.00-400.00 

125.50-  500.00 

200.00-  500.00 

50  and  over 

150.00-500.00 

200.00-  600.00 

300.00-  600.00 

1  The  range  of  figures  is  due  first  to  structural  difficulties,  second  to  the 
type  of  motor  panel  desired,  third  to  the  voltage,  and  fourth  to  the  circuit 
distance.  The  lower  figures  represent  the  minimum  structural  difficul- 
ties, with  fused  switches  in  an  iron  box  and  with  starting  device  mounted 
exposed  on  wall  to  side  of  motor,  220-volt  service  and  50-ft.  to  100-ft. 
circuit  distance.  The  higher  figures  represent  the  maximum  structural 
difficulties,  motor  panels  with  circuit-breakers,  110-volt  service  and  150-ft. 
to  300-ft.  circuit  distance.  The  figures  do  not  include  the  cost  of  motors, 
rheostats  and  regulators. 

TABLE  VII. — AVERAGE  COSTS  PER  OUTLET  FOR  WIRING  FOR  LAMPS  IN 

NEW    BUILDINGS1 


Outlets 

Exposed 

porcelain 

Wood 

Metal 

conduit 

molding 

molding 

Light  .... 

$4  .  00-S8  .  00 

$5.00-$10.00 

$8.00-$16.00 

$7.00-$14.00 

Switch.  . 

.  1   5.00-10.00 

6.00-  12.00 

9.00-  18.00 

8.00-  16.00 

Wall  receptacle  5.00-10.00 

6.00-  12.00 

9.00-  18.00 

8.00-  16.00 

Floor  receptacle  

7.00-14.00 

8.00-  16.00 

11.00-  22.00 

10.00-  20.00 

Fan  

6.00-12.00 

7.00-  14.00 

10.00-  20.00 

9.00-  18.00 

Iron  

9.00-18.00 

10.00-  20.00 

13.00-  26.00 

12.00-  24.00 

Electric  heater  7.00-14.00 

8.00-  16.00 

11.00-  22.00 

10.00-  20.00 

Vacuum  control  switch2  12.00-24.00 

13.00-  26.00 

16.00-  32.00 

15.00-  30.00 

1  For  use  where  the  total  cost  of  the  work  is  about  $2,000.     For 
residences  the  lower  figures  should  be  used.     For  public  buildings,  such 
as  banks,  office  buildings,  churches  and  the  like,  a  figure  midway  be- 
tween the  range  of  figures  given  should  be  used.     Where  best  grade  of 
material  and  workmanship  is  required  the  higher  figures  should  be  used. 
Prices   do  not  include  costs  of  fixtures  or  appliances,  but  do  include 
switches   and   receptacles.     For  wiring  old  buildings  where  porcelain 
work  and  conduit  work  is  concealed  the  figures  given  should  at  least  be 
doubled.     If  porcelain  or  conduit  work  is  to  be  installed  exposed  in 
either  old  or  new  buildings,  the  figures  should  be  increased  at  least  25 
per  cent.,  the  difference  of  cost  depending  upon  the  purpose  for  which 
the  building  is  or  was  designed. 

2  Includes  automatic  starter  at  motor. 


22 


THE  ELECTRICAL  CONTRACTOR 


TABLE  VIII. — AVERAGE  COSTS  FOR  SIGNAL  SYSTEMS  RUN  CONCEALED 

IN    NEW    BUILDINGS1 

Costs  per  outlet   (connected 


Bell  wiring 

as  one  outlet) 

Porcelain 

Conduit 

Per  push-button  and  bell 

$6.00 

4.00 

$12.00 
8.00 

Per  drop  on  annunciator  

1  For  work  on  old  buildings  the  figures  given  above  should  be  doubled- 
The  cost  of  push-buttons,  bells  and  annunciators  is  included. 

TABLE  IX. — AVERAGE  COSTS  OF  PRIVATE  TELEPHONES 


Porcelain 


Per  desk  telephone . 
Per  wall  telephone  . 


$30-$50 
25-  45 


Conduit 

$40-$60 
35-  55 


TABLE  X. — AVERAGE  COSTS  OF  PUBLIC  TELEPHONES  IN  NEW  BUILDINGS, 
CONCEALED  WORK* 


Conduit 


Per  outlet.  . 


$5 . 00-$ 15 . 00 


1  Cost  of  wires  is  not  included  since  the  electrical  contractor  very  seldom 
does  the  wiring.  The  range  of  the  figures  is  due  to  variations  in  the  dis- 
tances between  outlets.  Instruments  are  assumed  to  be  furnished  and 
installed  by  the  telephone  company. 

TABLE  XI. — COST  OF  INSTALLING  MISCELLANEOUS  WoRK1 


Apparatus 


Porcelain 


Conduit 


Time  clocks 

$30  00-$45  00 

$35  .  00-$50  .  00  per  clock 

Time  stamps  
Fire  alarms  
Watchmen's  stations  

65.00-  85.00 
20.00-  30.00 
25.00-  35.00 

70  .  00-  90  .  00  per  stamp 
25  .  00-35  .  00  per  alarm 
30  .  00-  40  .  00  per  station 

1  The  range  of  the  figures  given  above  is  due  to  differences  in  the  grades 
of  workmanship  and  materials.  For  old  buildings  the  figures  given 
should  be  increased  from  25  to  50  per  cent.  These  figures  include  the 
cost  of  apparatus  as  well  as  the  cost  of  all  conductors,  conduits  and  labor. 


COST-KEEPING 


23 


WEEK  ENDING 

1  LABOR 
>£'CONDT. 

1  LABOR 
2"CONDT. 

LABOR 
^C14.  D.W 

O  * 

3s 

LABOR 
OUTLET  BOXES 

LABOR 
FIX.SUP'P. 

LABOR 
SW.BOXES 

LABOR 

SWS. 

LABOR 
PANEL  BOXES 

LABOR 
PANEL  B'D. 

LABOR 
DOOR  &  TRIM 

LABOR 
METER  B'D. 
&SW. 

TOTAL 
LABOR 

yzc. 

2  C. 

14  D. 

%w. 

LT.B. 

F.S. 

SW.B 

sw. 

P.B.B 

P.B. 

D.&T 

M.B. 

. 

FIG.  5. — Unit  cost  sheet  compiled  by  clerk. 


24  THE  ELECTRICAL  CONTRACTOR 

It  is  essential  for  the  contractor  to  know  the  unit  costs 
of  labor  for  performing  the  various  operations  entering 
into  the  execution  of  any  wiring  contract  as  the  method 
previously  described  will  not  give  this  information. 

The  labor  item  in  the  electrical-contracting  business 
is  subject  to  changes  due  to  variations  in  the  price  of 
labor  resulting  from  increases  or  decreases  of  rates  and 
to  variations  in  the  unit  costs  with  the  nature  of  the 
building  construction.  The  latter  variations  may 
amount  to  100  per  cent,  or  more. 

The  cost  of  labor  can  be  determined  with  a  fair  degree 
of  accuracy  for  buildings  of  various  types,  such  as  those 
of  brick-and-joist  construction,  structural-steel  construc- 
tion with  terra-cotta  or  concrete  floors,  and  reinforced- 
concrete  construction,  by  the  following  method,  which 
may  be  worked  out  as  elaborately  as  necessary  and  made 
to  cover  not  only  the  labor  required  for  installing  dif- 
ferent sizes  of  conduit,  wires,  etc.,  but  also  the  labor 
required  for  connecting  various  sizes  of  wires  to  switch- 
boards, dynamos,  lugs,  etc. 

When  a  contract  is  secured  in  which  the  unit  price  of 
labor  for  certain  parts  of  the  work  is  not  accurately 
known  to  the  contractor,  this  information  being  desired 
for  future  use,  he  should  endeavor  to  obtain  these  data 
by  having  a  sheet  such  as  shown  in  Fig.  5  prepared  for 
his  pay-roll  clerk.  A  copy  of  this  sheet  should  be  given 
to  the  foreman  on  the  job  with  instructions  to  mark 
his  time  sheets  according  to  the  symbols  for  the  labor 
items  as  shown  in  Fig.  5,  the  time  sheet  thus  marked 
being  shown  in  Fig.  6. 

At  the  end  of  the  week  the  pay-roll  clerk  inserts  on 
his  unit-cost  sheet  the  amount  of  money  expended  dur- 
ing that  week  for  the  various  labor  items  on  the  job 


COST-KEEPING 


25 


Pom  8-W-6J 

TIME 

I  y-i-  H  8.  H.  L 
_..___•                                                    Wf  fi(  f^  fling  ,.,                M 

Notice  —  Pay  Roll  close.  Wednesdays.    Time  not  then  reported,  will  not  be  paid  until  the 
-  following  week.     Hours:8  to  12  A.M.    12.30  to  4.SO  P.M. 
KELLER-PIKE  CO. 

Hour 

DESCRIPTION  OF  WORK 

EXPENSES 

1 

^ 

72."  C 

' 

1 

fy 

2*  C 

ff- 

>5//r    &. 

1 

1 

Tuesday 

! 

£ 

/j  * 

J? 

Total 

/(, 

«®-.  Do  Not  Write  la  Sp*ce  Below  -®8l       Signature    &&*•  Am*2£^ 

/I 

Job                                         Hw.                         <^xp. 
^                 si 

Total       —  "~* 

MrtitAJLAtL*^  Unfits  &0,          Ik                   — 

ETP.        "~~~* 

FIG.  6. — Time  sheets  showing  symbols  for  labor  items. 


26  THE  ELECTRICAL  CONTRACTOR 

under  way,  the  total  of  these  items  equaling  the  total 
pay-roll  for  that  job.  This  process  is  carried  on  until 
the  completion  of  the  work,  at  which  time  the  total  labor 
for  each  item  is  ascertained.  Dividing  the  total  labor 
for  installing  a  certain  material  by  the  total  amount  of 
the  materials  installed,  as  ascertained  from  the  con- 
tract ledger,  a  unit  price  is  obtained  for  installing  that 
material. 

It  is  very  often  desirable,  however,  to  know  what  the 
unit  price  of  labor  is  at  the  end  of  each  week,  especially 
if  the  job  is  some  distance  from  the  contractor's  office 
and  is  visited  by  his  superintendent  only  once  or  twice 
during  the  progress  of  the  work.  This  can  be  accom- 
plished by  the  use  of  material  sheets  (Fig.  7)  issued  to 
the  foreman.  Taking,  for  example,  the  report  on  con- 
duit work,  the  foreman  fills  out  the  lines  marked  A,  B, 
C  and  D  for  the  first  week,  after  which  only  the  lines 
A,  B  and  C  are  filled  out. 

The  line  A  designates  the  job.  The  line  D,  which  is 
filled  out  only  when  the  first  slip  is  issued,  indicates 
the  amount  of  conduit  on  the  job  at  the  time  the  foreman 
arrives,  while  the  line  5,  which  is  filled  in  by  the  fore- 
man every  week,  indicates  the  conduit  received  during 
that  week.  Now,  the  line  C,  which  is  filled  out  by  the 
foreman  every  week,  indicates  the  amount  of  conduit  on 
hand  at  the  end  of  the  week.  Hence,  the  sums  of  the 
amounts  of  materials  entered  on  the  lines  B  and  D  minus 
the  amounts  entered  on  C,  that  is,  B  -\-  D  —  C,  for  the 
first  week  indicate  the  amounts  of  the  different  sizes 
of  conduit  installed  during  that  week. 

After  the  first  week  the  sums  of  the  amounts  of  con- 
duit along  the  line  D  of  the  first  week's  report  and  along 
the  line  B  of  all  subsequent  weekly  reports,  minus  the 


COST-KEEPING 


27 


REPORT  ON  CONDUIT  WORK 

THE  FIRST  WEEK  THE  FOREMAN  WILL  FILL  OUT  THE  LINES  A.  B.  C  AND  O.  AFTER  THAT  THE  LINES  A.  B  ANO  C  ONLY.  KELLER-PIKE  CO. 

Z 

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REPORT  ON  WIRE  WORK 

L  FILL  OUT  THE  LINES  A.  B.  C  AND  D.  AFTER  THAT  THE  LINES  A.  B  AND  C  ONLY.  KELLER-PIKE  CO. 

1 

2 

i 

5 

i 

* 

REPORT  ON  OUTLET  WORK 

THE  FIRST  WEEK  THE  FOREMAN  WILL  FILL  Our  THE  LINES  A.  B.  C.  AND  D.  AFTER  THAT  THE  LINES  A.  a  ANO  C  ONLY.  KELLER-PIKE  CO. 

z 

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0 

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28  THE  ELECTRICAL  CONTRACTOR 

amounts  along  the  line  C  of  the  last  report,  indicate  the 
amounts  of  the  different  sizes  of  conduit  installed  up 
to  the  time  of  the  last  report. 

The  labor  costs  from  the  weekly  time  sheet  (Fig.  6) 
are  then  inserted  along  the  line  marked  ' 'labor  cost," 
and  the  unit  prices  are  accurately  figured  and  placed 
along  the  line  marked  " price  per  unit."  If  the  price 
per  unit  for  any  item  is  higher  than  the  estimated  price, 
the  head  of  the  construction  department  indicates  this 
by  placing  a  red  cross  opposite  the  particular  item  to 
which  he  desires  to  call  the  attention  of  the  superin- 
tendent. The  latter  immediately  investigates  the  mat- 
ter, reporting  on  any  possible  causes  for  the  increased 
costs  and  on  the  possibility  of  reducing  the  unit 
price. 

This  same  process  is  carried  out  for  wire  work  and 
outlet  work.  In  the  usual  installation  these  items  of 
conduit  work,  wire  work  and  outlet  work  are  by  far  the 
largest  portion  of  the  labor  item,  so  that  the  work  on 
signal  systems,  bells,  etc.,  can  be  neglected.  Otherwise 
the  cost  involved  for  ascertaining  unit  prices  on  the 
minor  work  would  far  overbalance  the  benefits  of  know- 
ing these  particular  labor  costs. 

In  Tables  XII  to  XXIX  as  obtained  by  the  above 
method  are  given  the  unit  costs  of  labor.  The  data, 
however,  cannot  be  considered  general  in  their  applica- 
tions, for  conditions  vary  widely  in  the  electrical  con- 
tracting field.  Every  contractor  should  make  his  own 
tables  and  curves,  utilizing  his  records  for  the  purpose. 
In  all  the  following  tables  it  is  assumed  that  the  rates 
for  labor  are  55  cts.  per  hour  for  foremen,  45  cts.  per 
hour  for  wiremen,  and  25  cts.  per  hour  for  helpers. 
All  figures  given  include  an  allowance  for  what  has  been 


COST-KEEPING 


29 


found  to  be  necessary  supervision  by  the  foreman  in  the 
class  of  work  under  consideration. 


TABLE  XII. — COST  PER  KILOWATT  FOR  ERECTING  BELTED  GENERATORS 


Size  in  kw. 

Normal 
condition 

Easy 

Difficult 

Cost  of 
painting 

1     -  5 

$1.00 

$0.75 

$1.50 

$0.60 

5     -12^ 

1.00 

0.75 

1.50 

0.60 

12^-25  " 

1.00 

0.75 

1.50 

0.50 

25     -50 

1.00 

0.75 

1.50 

0.40 

75 

0.80 

0.60 

1.25 

0.30 

100 

0.75 

0.60 

1.20 

0.25 

150 

0.60 

0.50 

0.90 

0.20 

200 

0.50                0.40 

0.80 

0.18 

300 

0.40                0.30 

0.60 

0.15 

500 

0  30                0  20 

0  50 

0  12 

TABLE    XIII.— COST    PER    KILOWATT    OF    FOUNDATIONS    FOR    BELTED 

GENERATORS1 


Size  in  kw. 


Normal  condition 


Easy 


Difficult 


1-5 

$2.00 

$1.50 

$3.00-$4.00 

5  -12K 

2.50 

2.00 

3.75-  5.00 

12^-25 

2.00 

1.50 

3.00-  4.00 

25  -50 

1.50 

1.00 

2.25-  3.25 

75 

1.20 

0.85 

1.80-  2.80 

100 

1.00 

0.75 

1.50-  2.50 

150 

0.85 

0.60 

1.25-  2.25 

200 

0.75 

0.60 

1.00-  2.00 

300 

0.60 

0.50 

0.90-  1.80 

500            0.50 

0.40 

0.75-  1.50 

1  The  items  under  this  heading  include  the  cost  of  labor  and  materials, 
which  is  the  usual  method  of  estimating  this  class  of  work.  The  figures 
are  based  on  the  average  cubical  contents  of  foundations  specified  by 
generator  makers.  If  the  electrical  contractor  is  to  furnish  the  belt  or 
belts,  the  labor  for  putting  them  in  place  should  be  included. 


30  THE  ELECTRICAL  CONTRACTOR 

TABLE  XIV. — LABOR  FOR  ERECTING  SWITCHBOARD  PANELS 


Dynamo  panel 
without 
sub-base 

Dynamo  panel 
with 
sub-base 

Feeder  panel 
without 
sub-base 

Feeder  panel 
with 
sub-base 

Cost  per  panel  

$10.00 

$12.00 

$12.00 

$15.00 

TABLE   XV. — LABOR   PER  LEAD   FOR   CONNECTING    SWITCHBOARD   AND 
DYNAMO  LEADS1 


Size,  B.  &  S. 

Paper  and  lead 

Rubber  and  lead 

Rubber  or 
slow-burning 
insulation 

14-8 

$0.33 

$0.30 

$0.21 

6 

0.45 

0.41 

0.28 

5 

0.55 

0.50 

0.33 

4 

0.66 

0.60 

0.40 

3 

0.80 

0.72 

0.49 

2 

0.87 

0.79 

0.53 

1 

0.92 

0.84 

0.56 

0 

1.00 

0.90 

0.60 

00 

1.04 

0.94 

0.63 

000 

1.08 

0.98 

0.65 

0000 

1.14 

1.03 

0.69 

Circ.  mils 

250,000 

1.18 

1.08 

0.72 

300,000-350,000 

1.34 

1.22 

0.78 

400,000-450,000 

1.43 

1.30 

0.84 

500,000-550,000 

1.60 

1.44 

0.90 

600,000-650,000 

2.10 

1.90 

1.00 

700,000-750,000 

2.50 

2.25 

1.25 

800,000-850,000 

2.95 

2.65 

1.50 

900,000-950,000 

3.30 

3.00 

1.75 

1,000,000 

3.75 

3.40 

2.00 

1  These  figures  are  the  labor  costs  for  soldering  cables  into  lugs  at  the 
switchboard  and  generators,  also  for  soldering  light  and  power  cables  into 
lugs  of  switches  on  the  switchboard.  They  include  the  cost  of  arranging 
the  cables  in  a  neat  and  workmanlike  manner  at  these  locations. 


COST-KEEPING  31 

TABLE  XVI. — LABOR  COSTS  (IN  CENTS)  PER  FOOT  OF  CONDUIT  WORK[ 


Size  of 
conduit 

Steel-terra-cotta 
construction 

Concrete 
construction 

Slow-burning 
construction 

Exposed 

Concealed 

Exposed 

Concealed 

Exposed 

Concealed 

Small 
am't 

Large 
am't 

Small 
am't 

Large 
am't 

Small 
am't 

Large 
am't 

Small 
am't 

Large 
am't 

Small 
am't 

Large 
am't 

Small 
am't 

Large 
am't 

\<N  V* 

rH\  C0\ 

7 
8 
9 

6 

7 
8 

6 

7 
8 

4 
5 
6 

8 
9 
10 

I 

9 

7 
8 
9 

5 
6 

7 

6 

7 
8 

5 
6 

7 

6 

7 
8 

4 

5 
6 

1^| 

10 

9 

9 

7 

11 

10 

10 

8 

9 

8 

9 

7 

IK 

11 

10 

10 

8 

12 

11 

11 

9 

10 

9 

10 

8 

2 

12 

11 

11 

9 

15 

12 

12 

10 

12 

10 

11 

9 

2^ 

15 

12 

12 

10 

20 

15 

15 

12 

15 

12 

12 

10 

3 

20 

15 

15 

12 

25 

20 

20 

15 

20 

15 

15 

12 

31^ 

25 

20 

20 

15 

30 

25 

25 

20 

25 

20 

20 

15 

4 

30 

25 

30 

20 

40 

30 

30 

25 

30 

25 

30 

20 

1  The  figures  given  in  the  table  of  costs  for  conduit  work  are  for  work  in 
new  buildings  and  include  the  labor  cost  of  preparing  for  and  running 
rigid  conduit  per  foot,  as  well  as  the  labor  on  junction  boxes.  If  conduits 
are  to  be  installed  in  old  buildings,  the  cost  figures  would  be  considerably 
greater  than  those  given  in  the  table,  the  percentage  of  increase  depending 
on  the  conditions.  However,  for  concealed  work  in  existing  buildings 
flexible  conduit  (see  Table  XVII)  is  generally  used  in  order  to  do  as  little 
tearing  out  as  possible. 

TABLE  XVII. — FLEXIBLE-CONDUIT  LABOR  COSTS  PER  FOOT  FOR  CON- 
CEALED WORK  IN  EXISTING  BuiLDiNGS1 


Size,  inches 

Slow-burning  construction 

Fire-proof  construction 

H 

$0.08 

$0.10 

3A 

0.09 

0.11 

l 

0.10 

0.12 

m 

0.12 

0.15 

V/2 

0.15 

0.20 

2 

0.20 

0.30 

2K 

0.30 

0.40 

3 

0.40 

0.50 

1  The  figures  include  cost  of  preparing  for  and  running, 
difference  in  cost  whether  the  amount  is  large  or  small. 


There  is  little 


32 


THE  ELECTRICAL  CONTRACTOR 


TABLE  XVIII. — COST  PER  FOOT  OF  FISHING  CONDUITS  AND  PULLING 

WIRES1 


Size 

One  wire  per  conduit 

Two  or  more   wires  per 
conduit 

B.  &S. 

14 

$0.005 

$0.004 

12 

0.006 

0.004 

10 

0.0065 

0.005 

8 

0.0075 

0.006 

6 

0.0085 

0.0065 

5 

0.01 

0.007 

4 

0.013 

0.0075 

3 

0.016 

0.008 

2 

0.023 

0.013 

1 

0.025 

0.016 

0 

0.03 

0.02 

00 

0.04 

0.023 

000 

0.045 

0.025 

0000 

0.05 

0.03 

Circ.  mil. 

250,000 

0.055 

0.04 

300,000-350,000 

0.065 

0.045 

400,000-450,000 

0.075 

0.055 

500,000-550,000 

0.08 

0.065 

600,000-650,000 

0.09 

0.075 

700,000-750,000 

0.09 

0.085 

800,000-850,000 

0.10 

0.09 

900,000-950,000 

0.11 

0.09 

1,000,000 

0.12 

0.10 

1,250,000 

0.12 

0.10 

1,500,000 

0.12 

0.10 

1,750,000 

0.12 

0.10 

2,000,000 

0.12 

0.10 

1  These  figures  are  for  large  amounts  of  rigid  or  flexible  conduit  in 
either  new  or  existing  buildings.  For  small  amounts  the  figures  should 
be  increased  from  10  to  30  per  cent. 


COST-KEEPING 


33 


TABLE  XIX. — LABOR  COST  OF  INSTALLING  PANELBOARDS  AND  BOXES 


Boxes 

Number  of 
circuits 

New  buildings 

Old  buildings 

Panels  in- 
stalled and 
connected 

Doors 
and 
trim 

Exposed 

Concealed 

Exposed 

Concealed 

1-  6 

$1.00 

$1.00 

$1.00 

$2.00 

$1.00 

$0.40 

8-10 

1.25 

1.25 

1.25 

2.25 

1.50 

0.50 

10-14 

1.50 

1.50 

1.50 

2.50 

2.00 

0.60 

16-20 

2.00 

2.00 

2.00 

3.00 

3.00 

0.75 

24-30 

2.50 

2.50 

2.50 

4.00 

4.00 

1.00 

TABLE  XX. — LABOR  COST  OF  INSTALLING  AND  CONNECTING  MOTORS* 

Mounting 


J.±p.    Ul     lllUtUI 

Floor 

Ceiling 

Wall 

1    -  2 

$1.00 

$1.50 

$1.50 

3-5 

3.00 

4.50 

3.50 

7y2-W 

6.00 

9.00 

7.50 

15 

10.00 

15.00 

12.00 

20 

15.00 

22.00 

18.00 

25 

20.00 

30.00 

24.00 

35 

25.00 

37.00 

30.00 

50 

35.00 

51.00 

42.00 

75 

50.00 

75.00 

60.00 

100 

75.00 

110.00 

90.00 

150 

100.00 

150.00 

120.00 

200 

150.00 

225  .  00 

180.00 

1  Includes  labor  on  supports. 


TABLE  XXI. — COST  OF  LABOR  FOR  INSTALLING  AND  CONNECTING 
SWITCHES  AND  RECEPTACLES 


Single-pole  switches  

$0.20 

Door  switches  

$0.20 

Double-pole  switches  

0.25 

Wall  receptacles  

0.20 

Three-way  switches  

0.30 

Floor  receptacles  

0.30 

Four-way  switches  

0.25 

34  THE  ELECTRICAL  CONTRACTOR 

TABLE  XXII. — LABOR  COST  OF  INSTALLING  OUTLET  BOXES  AND  SUPPORTS 


Type  of  outlet 

Old  buildings 

New  buildings 

Steel  and 
terra-cotta 

Slow- 
burning 

Concrete 

Steel  and 
terra-cotta 

Slow- 
burning 

Light  outlets 

$0.35 
0.10 
0.35 
0.35 
0.50 

$0.30 
0.10 
0.30 
0.30 
0.45 

$0.30 

0.10 
0.30 
0.30 
0.60 

$0.25 
0.10 
0.25 
0.25 
0.40 

$0.20 
0.10 

0.20 
0.20 
0.30 

Fixture  supports  

Switch  boxes  
Wall-receptacle  boxes.  .  . 
Floor-receptacle  boxes  .  . 

TABLE     XXIII. — LABOR     COSTS     FOR     INSTALLING 

APPARATUS 


MOTOR-CONTROL 


H.p.  of  motor 

Switch  and  rheostat 

Controlling  panel  com- 
plete,  switch,    rheostat, 
etc. 

1-2 

$0.75 

$2.00 

3-5 

1.00 

3.00 

7M-10 

2.00 

4.00 

15 

2.50 

5.00 

20 

3.00 

6.00 

25 

3.50 

7.00 

35 

4.50 

9.00 

50 

6.00 

11.00 

75 

8.00 

13.00 

100 

10.00 

15.00 

150 

12.00 

17.00 

200 

15.00 

20.00 

COST-KEEPING 


35 


TABLE  XXIV. — LABOR  PER  FOOT  OF  WIRE  FOR  INSTALLING  CONCEALED 
KNOB-AND-TUBE  WORK 


Size  of  wire,  B.  &  S. 

New  buildings 

Old  buildings 

14 

$0.01 

$0.03 

12 

0.01 

0.03 

10 

0.01 

0.03 

8 

0.012 

0.035 

6 

0.015 

0.045 

5 

0.018 

0.055 

4 

0.02 

0.06 

3 

0.023 

0.07 

2 

0.025 

0.075 

1 

0.03 

0.09 

0 

0.03 

0.09 

00 

0.035 

0.11 

000 

0.035 

0.11 

0000 

0.04 

0.12 

36 


THE  ELECTRICAL  CONTRACTOR 


TABLE  XXV. — LABOR  PER  FOOT  OF  WIRE  FOR  INSTALLING  EXPOSED 
KNOB-AND-TUBE  WORK1 


Size  of  wires,  B.  &  S. 

Running  wire  after 
backboard  or  buttons 
are  erected 

Erecting  backboard 
or  buttons 

14 

$0.015 

$0.02 

12 

0.015 

0.02 

10 

0.015 

0.02 

8 

0.017 

0.025 

6 

0.02 

0.03 

5 

0.02 

0.035 

4 

0.023 

0.04 

3 

0.025 

0.045 

2 

0.03 

0.05 

1 

0.035 

0.06 

0 

0.035 

0.07 

00 

0.04 

0.08 

000 

0.045 

0.09 

0000 

0.045 

0.10 

1  When  good  knob-and-tube  work  is  installed  in  new  and  old  buildings 
the  labor  at  outlets  will  be  practically  the  same  as  given  in  Table  XXII 
under  the  several  headings,  and  the  labor  for  switches  and  receptacles 
should  be  exactly  the  same  as  in  Table  XXI. 


TABLE    XXVI. — LABOR    COST    PER    FOOT    FOR    INSTALLING    MOLDING 


Wires 

\\T          ,             ,  ,. 

TVT      h      1               IrT 

Number 

Size,  B.  &  S. 

2 

14 

$0.04 

$0.08 

2 

12 

0.05 

0.08 

2 

10 

0.06 

0.08 

2 

8 

0.07 

2 

6 

0.08 

1  Metal  molding  is  not  made  in  sizes  larger  than  for  No.  10  wires,  and 
wood  molding  is  seldom  used  for  wires  larger  than  No.  6.  The  labor  at 
outlets  with  molding  is  practically  the  same  in  the  case  of  both  wood  and 
metal-molding  construction.  Tables  similar  to  Tables  XXI  and  XXII 
can  hence  be  made. 


COST-KEEPING  37 

TABLE  XXVII. — COST  OF  POLE-LINE  CONSTRUCTION 


Labor  item 

Description 

Cost 

Shaving  poles  

25-ft.  pole 

$0.60-$  1.20 

30-ft.  pole 

0.80-  1.60 

35-ft.  pole 

1.00-  2.00 

40-ft.  pole 

1.20-  2.40 

50-ft.  pole 

1.40-  2.80 

Erecting  wood  poles  

25-ft.  pole 

0.90-  2.70 

30-ft.  pole 

1.20-  3.60 

35-ft.  pole 

1.80-  5.40 

40-ft.  pole 

2.70-  8.10 

50-ft.  pole 

3.90-11.70 

Erecting  iron  poles  

25-ft.  pole 

2.00-  8.00 

30-ft.  pole 

3.00-12.00 

35-ft.  pole 

5.00-20.00 

40-ft.  pole 

8.00-32.00 

50-ft.  pole 

12.00-48.00 

Digging  holes 

25-ft.  pole 

0.60-  3.00 

30-ft.  pole 

0.75-  3.75 

35-ft.  pole 

0.90-  4.50 

40-ft.  pole 

1.05-  5.25 

50-ft.  pole 

1.20-  6.00 

Stepping  poles 

25-ft.  pole 

0.50-  1.00 

30-ft.  pole 

0.75-  1.50 

35-ft.  pole 

1.00-  2.00 

40-ft.  pole 

1.25-  2.50 

50-ft.  pole 

1.50-  3.00 

Guying  poles 

25-ft.  pole 

3.00-  9.00 

30-ft.  pole 

4.00-12.00 

35-ft.  pole 

5.00-15.00 

40-ft.  pole 

6.00-18.00 

50-ft.  pole 

7.00-21.00 

Erecting  cross-arms,  braces,  pins  and 

2-pin  cross-arm 

$0.50-11.00 

insulators  

3-pin  cross-arm 

0.60-  1.20 

4-pin  cross-arm 

0.70-  1.40 

6-pin  cross-arm 

0.90-  1.80 

8-pin  cross-arm 

1.10-  2.20 

38  THE  ELECTRICAL  CONTRACTOR 

TABLE  XXVII. — COST  OF  POLE-LINE  CONSTRUCTION — (Continued) 


Labor  item 

Description 

Cost 

Stringing  wire,  triple-braid,  weather- 

proof, per  1,000  ft  

No.        8 

$2  .  50-$5  .  00 

No.        6 

2.60-  5.20 

No.        5 

2.80-  5.60 

No.        4 

3.10-  6.20 

No.        3 

3.50-  7.00 

No.        2 

4.00-  8.00 

No.        1 

4.60-  9.20 

No.        0 

5.20-10.40 

No.      00 

6.00-12.00 

No.    000 

6.90-13.80 

, 

No.  0000 

7.90-15.80 

TABLE  XXVIII. — LABOR  COSTS  PER  FOOT  FOR  LAYING  DUCTS 


Item 


Cost 


Laying  duct  and  cementing  joint: 

Single-way 

Two-way 

Three-way 


Four-way 

Six-way 

Nine-way 


$0.03  -$0.06 
0.05  -  0.10 
0.08  -  0.16 

0.10  -  0.20 
0.14  -  0.28 
0.20  -  0.40 


Laying  conduit  or  pipe : 

3^-in.  conduit 

%-in.  conduit 

1  -in.  conduit 

1^-in.  conduit 

1^2-in.  conduit 


2  -in.  conduit. 
2^2-in.  conduit. 

3  -in.  conduit. 

4  -in.  conduit. 


$0.03  -$0.05 
0.04  -  0.06 
0.05  -  0.07 
0.06  -  0.08 
0.065-  0.09 

0.07  -  0.10 
0.08  -  0.12 
0.09  -  0.14 
0.12  -  0.18 


COST-KEEPING  39 

TABLE  XXIX. — LABOR  COSTS  FOR  PULLING  IN  AND  SPLICING  CABLES 


Size,  B.  &  S.  or  circ.  mil 

Pulling  cable,  cost 
per  ft. 

Splicing  cables,  cost 
per  splice 

Single-conduit  : 

No.                         14 

$0.02 

$1.10 

12 

0.025 

1.20 

10 

0.03 

1.30 

8 

0.035 

1.40 

6 

0.04 

1.55 

5 

0.045 

1.70 

4 

0.05 

1.85 

3 

0.055 

2.00 

2 

0.06 

2.20 

1 

0.0625 

2.40 

0 

0.065 

2.60 

00 

0.0675 

2.80 

000 

0.07 

3.05 

0000 

0.0725 

3.30 

250,000 

0.075 

3.55 

300,000 

0.0775 

3.80 

350,000 

0.08 

4.10 

400,000 

0.085 

4.40 

450,000 

0.09 

4.70 

500,000 

0.095 

5.00 

550,000 

0.10 

5.30 

600,000 

0.105 

5.60 

650,000 

0.11 

5.90 

700,000 

0.115 

6.20 

750,000 

0.12 

6.50 

800,000 

0.125 

6.80 

850,000 

0.13 

7.10 

900,000 

0.14 

7.40 

950,000 

0.15 

7.70 

1,000,000 

0.16 

8.00 

40 


THE  ELECTRICAL  CONTRACTOR 


TABLE  XXIX. — LABOR  COSTS  FOR  PULLING  IN  AND  SPLICING  CABLES. 

— (Continued] 


Size,  B.  &  S.  or  circ.  mil 


Pulling  cable,  cost     '  Splicing  cables,  cost 
per  ft.  per  splice 


Duplex  : 

No. 

14 

$0.03 

$1.55 

12 

0.04 

1.80 

10 

0.045 

1.95 

8 

0.05 

2.10 

6 

0.06 

2.30 

5 

0.07 

2.55 

4 

0.08 

2.80 

3 

0.09 

3.00 

2 

0.09 

3.30 

1 

0.095 

3.60 

0 

0.10 

3.90 

00 

0.105 

4.20 

* 

000 

0.11 

4.65 

0000 

0.115 

5.00 

250,000 

0.12 

5.40 

300,000 

0.125 

5.80 

350,000 

0.13 

6.20 

400,000 

0.135 

6.60 

450,000 

0.14 

7.10 

500,000 

0.15 

8.00 

Triplex  : 

No. 

14 

$0.04 

$2.20 

12 

0.045 

2.40 

10 

0.05 

2.60 

8 

0.055 

2.80 

6 

0.065 

3.10 

5 

0.075 

3.40 

4 

0.09 

3.70 

3 

0.10 

4.00 

2 

0.11 

4.40 

1 

0.12 

4.80 

0 

0.13 

5.20 

00 

0.14 

5.60 

000 

0.15 

6.10 

0000 

0.16 

6.60 

The  figures  given  for  pulling  cable  do  not  include  rodding  or  fishing  of 
ducts,  which  varies  from  $0.005  to  $0.03  per  duct  foot. 


CHAPTER  IV 
ESTIMATES 

If  the  items  entering  into  architects'  and  engineers' 
specifications  were  always  given  in  succession  from 
point  of  supply  to  the  outlets,  the  chances  of  the  elec- 
trical contractor  omitting  items  in  his  estimate  would 
be  considerably  reduced.  Whether  or  not  the  architects 
or  engineers  write  their  specification  in  that  form,  the 
contractor  should  prepare  his  estimate  so. 

If  an  engine  is  to  be  installed  in  the  plant,  the  con- 
tractor's first  items  should  be  for  engines,  foundations, 
painting,  etc.  Next  should  come  the  item  for  genera- 
tors. If  these  be  belted  machines,  the  belts  could.be 
included  under  this  item.  Then  should  come  the  dy- 
namo cables  installed  and  connected  to  the  lugs  of  the 
dynamos  and  switchboard.  This  should  be  followed  by 
the  item  of  switchboards  installed  complete  with  in- 
struments, circuit-breakers,  etc.  This  would  practically 
complete  the  plant  unless  a  storage  battery  was  to  be 
installed.  A  miscellaneous  item  could  be  inserted  either 
at  this  point  or  under  the  general  expense  item  at  the 
end  of  the  estimate  covering  the  tests  and  if  necessary 
the  water  rheostat. 

The  estimate  should  then  include  the  following  items 
in  the  succession  here  given,  the  costs  of  both  material 
and  labor  being  entered  : 

Connection  of  power  and  light  feeders  to  switchboard. 
Flexible  tubing,  junction  box,  condulets,  etc. 
Power  feeders,  mains  and  submains. 

41 


42 


THE  ELECTRICAL  CONTRACTOR 


Power  panels,  boxes,  doors,  trim  and  fuses. 
Power  branches. 

Power  outlets,  such  as  switches,  starters  and  the  like,  erected  and 
connected,  wiring  between  switches,  starters,  etc.,  and  motors. 
Motors  and  foundations,  delivered,  erected  and  connected. 

This  would  complete  the  power  portion  of  the  esti- 
mate, and  the  lighting  portion  should  follow,  the  items 
being  taken  in  the  order  given  below: 

Light  feeders,  mains  and  submains. 
Panelboards,  panel  boxes,  doors,  trim  and  fuses. 
Branches. 
Outlets. 

Expenses,  cartage,  freight,  car  fare,  railroad  fare,  loss  of  time,  in- 
spection fees,  shanty,  telephone,  bond,  insurance  and  miscellaneous. 

The  same  method  should  be  followed  in  making  an  esti- 
mate for  telephone,  telegraph,  fire-alarm,  watchman's- 
clock,  time-clock,  annunciation  and  similar  systems. 

An  estimate  for  light  branches  according  to  this  detail 
method  would  appear  as  shown  in  Fig.  8. 

Page  3  Esimate  No.  10,576 


Item 

Labor  and  materials 

Unit  price 

Light  branches  

400  ft.  ^-in.  conduit,  loricated  

$0.06 

$24.00 

200  ft.  ?4-in.  conduit,  loricated  

0.07 

14.00 

600  ft.  No.  12  duplex,  N.E.C.S  

0.03 

18.00 

200  ft.  No.  12  single,  N.E.C.S  

0.015 

3.00 

Labor,  ^-in    conduit    *         ... 

0.08 

32.00 

Labor,  f4-in    conduit  .                    .... 

0.09 

18.00 

Labor,  No.  12  duplex           .        .    . 

0.01 

6.00 

Labor,  No    12  single.            

0.08 

1.60 

Supports,  etc     .    .        

3.40 

$120.00 

Outlets  

20  light  outlet  boxes,  T.  &  B  

0.20 

4.00 

Labor     .          

0.30 

6.00 

20  studs  or  supports,  T.  &  B  

0.15 

3.00 

Labor  

0.20 

4.00 

5  switch  boxes  

0.25 

1.25 

Labor  

0.30 

1.50 

5  switches,  D.P.,  Cutter  

0.80 

4.00 

Labor  

0.30 

1.50 

Bushings,  etc  

5.00 

30.25 

FIG.  8. — Applying  the  detail  method  to  branch  circuits. 


ESTIMATES 


43 


In  making  an  estimate  for  the  electrical  equipment 
in  say  a  large  institution  composed  of  several  similar 
size  buildings,  the  mains  in  a  number  of  cases  may  be  of 
the  same  size. 

As  time  is  generally  an  important  feature,  one  must 
be  prepared  to  save  all  unnecessary  detail  work,  which 
can  be  done  in  the  following  manner  without  effecting 
the  accuracy  of  an  estimate.  Take,  for  example,  the 
item  of  mains  in  an  estimate.  If  made  in  detail,  it  would 
be  as  shown  in  Fig.  9. 


Page  2 


Estimate  No.  10,176 


Item 

Labor  and  materials 

Unit  price 

Light   mains,   three- 

wire  

200  ft.  2-in.  conduit,  loricated  

$0.20 

$40  .  00 

3  2-in.  L's,  loricated  

0.30 

0.90 

3  2-in.  couplings,  loricated  

0.10 

0.30 

1  2-in.  condulet  (three-wire)  

2.00 

600  ft.  No.  0  D.B.,  N.E.C.S  

0.15 

90.00 

0  25 

50.00 

0.05 

30.00 

Supports,  junction  box,  etc  

9.00 

$222.20 

FIG.  9. — Applying  the  detail  method  to  mains. 


It  will  be  noted  that  the  total  cost  for  running  200 
ft.  of  main  consisting  of  three  No.  0  wires  is  $222.20, 
or  $1.10  per  foot.  The  contractor  could  prepare  tables 
of  unit  prices  for  all  items  in  an  estimate,  such  as  for 
two-wire  to  nine-wire  service  connections,  two-wire  to 
five-wire  mains,  two-wire  and  three-wire  branches,  etc., 
showing  their  cost  for  buildings  of  various  types  of 
construction.  The  disadvantage  of  this  method,  how- 
ever, is  that  a  change  in  price  of  materials  diminishes 
the  accuracy  of  the  tables. 


44  THE  ELECTRICAL  CONTRACTOR 

UNDERGROUND  CONSTRUCTION 

In  estimating  on  underground  construction  work,  a 
logical  method  should  likewise  be  used.  The  first  item 
to  be  considered  being  the  trench  work.  Under  this 
heading  the  following  items  should  be  included: 

Excavating. 

Concreting. 

Ducts  and  laying  of  same. 

Metal  bands,  burlap,  pitch,  etc.,  for  joints. 

Cables  and  installing  same. 

Refilling. 

Regrading  and  resodding. 

The  next  item  should  be  that  of  manholes.  Under 
this  heading  the  following  items  should  be  included: 

Excavating. 

Brick  or  concreting  work.    • 

Drains. 

Cable  racks. 

Splicing  of  cables. 

Manhole  covers. 

Refilling. 

With  the  addition  to  the  above  of  an  expense  item  an 
estimate  for  the  ordinary  underground-construction  job 
would  be  complete.  This  expense  item  in  some  cases 
is  considerable,  especially  where  underground  work  is 
installed  in  populated  district,  when  the  cost  of  a  watch- 
man, lanterns  and  refilling  of  same  and  boards  for 
covering  exposed  trench  work  during  the  night  must  be 
included. 

POLE-LINE  CONSTRUCTION 

The  first  heading  should  be  that  of  poles  (wood)  and 
should  include  the  following  items: 


ESTIMATES  45 

Digging  of  holes. 
Shaving  of  poles. 
Stepping  poles. 
Poles  and  erection  of  same. 

Refilling — and  if  in  a  city,  repairs  to  pavement,  curb,  etc.,  must 
be  included. 

The  next  item  should  be  that  of  wires.  Under  this 
heading,  the  following  items  should  be  included: 

Cross-arms  and  braces  including  erection  of  same. 

Pins  and  insulators. 

Wire  and  stringing  of  same. 

With  the  addition  to  the  above  of  an  expense  item  an 
estimate  for  the  ordinary  pole-construction  job  would  be 
completed.  In  large  work  of  this  type  numerous  addi- 
tional items  would  be  met  with,  such  as: 

Lightning  arrestors  and  grounding. 

Anchor  rods  and  guying. 

Transformers. 

Lamps,  brackets  and  cross-suspension. 


CHAPTER  V 

CALCULATING    WIRE    SIZES   FOR   DIRECT-CURRENT 

CIRCUITS 

The  subject  of  voltage  drop  is  one  to  which  many  elec- 
trical contractors,  architects  and  engineers  give  very 
little  attention.  It  is  for  this  reason  that  the  subject  of 
the  calculation  of  resistances,  voltage  drops  and  neces- 
sary sizes  of  wires,  etc.,  has  been  included  by  the  writer. 
The  information  given  on  these  subjects  is  by  no  means 
intended  by  the  writer  as  a  treatise  on  electric  wiring, 
but  rather  as  general  information  which  it  is  hoped  will 
be  of  some  value  to  electrical  contractors,  architects, 
engineers  and  owners. 

Some  of  the  formulas  with  which  the  writer  is  ac- 
quainted as  recommended  for  computing  voltage  drops 
are  not  applicable  to  all  systems  of  wiring.  In  many 
cases  it  is  found  that  contractors  are  almost  helpless 
when  it  is  necessary  to  compute  the  voltage  drop  in 
even  a  small-size  job.  As  a  result  lamps  in  many  installa- 
tions do  not  burn  at  maximum  efficiency  owing  to  ex- 
cessive voltage  drops.  It  is  with  the  hope  of  rendering 
the  calculation  of  voltage  drop  comparatively  easy  that 
the  following  discussion  of  voltage  drop  in  direct-current 
and  alternating-current  circuits  is  given. 

There  are  two  factors  that  should  be  considered  in 
laying  out  any  direct-current  circuit.  First,  the  heat 
loss,  which  depends  upon  the  value  of  the  current  and 
the  material  and  size  of  the  wire,  must  be  considered. 

46 


WIRE  SIZES  FOR  D.  C.  CIRCUITS  47 

The  amount  of  this  loss  in  watts  is  equal  to  the  product 
of  the  square  of  the  current  in  amperes  multiplied  by 
the  resistance  of  the  conductor  in  ohms,  or  C2R.  This 
heat  loss  is  very  seldom  computed,  as  the  Underwriters' 
requirements  are  intended  to  keep  this  loss  well  within 
the  limit  of  safety.  The  carrying  capacities  of  the 
various  sizes  of  wire,  as  specified  in  the  National  Elec- 
trical Code,  are  such  as  to  keep  the  temperature  rise 
within  safe  limits  for  the  type  of  insulation  employed. 

A  size  of  wire,  therefore,  should  be  figured  that  will 
meet  the  pressure  requirement  and  at  the  same  time 
meet  the  requirements  of  the  code  in  regard  to  safe 
carrying  capacities. 

By  Ohm's  law  the  allowable  resistance  in  any  wire  to 
meet  the  voltage-drop  requirement  can  be  found  by 
dividing  the  permissible  loss  in  volts  by  the  current, 
R  =  E/C,  the  resistance  being  in  ohms.  For  example, 
what  should  be  the  resistance  of  a  wire  in  which  a  cur- 
rent of  100  amp.  is  flowing,  to  give  a  voltage  drop  of 
5  volts? 

R  =  5  -T-  100  =  0.05  ohm 

Suppose  the  distance  to  be  250  ft.  Then  the  circuit 
distance,  assuming  it  to  be  a  two-wire  system,  is  500  ft. 
A  size  of  wire  is  required  which  will  have  a  resistance 
of  0.05  ohm  for  a  500-ft.  length.  The  writer  employs 
tables  which  give  the  resistance  of  all  sizes  of  wire  in 
lengths  of  from  10  ft.  to  1,000  ft.  at  10-ft.  intervals.  A 
sample  table  is  given  in  Table  XXX.  Complete  tables 
of  the  same  or  similar  nature  can  be  found  in  numerous 
handbooks,  text-books  and  wire  manufacturers'  litera- 
ture. When  tables  such  as  these  are  examined  it  will 
be  found  that  the  size  of  wire  would  be  No.  0.  Tables 


48 


THE  ELECTRICAL  CONTRACTOR 


as  indicated  should  be  made  or  obtained  for  all  sizes  of 
wire  used  in  practice. 

TABLE  XXX. — RESISTANCE  IN  OHMS  OF  No.  0  B.  &  S.  GAGE  HARD- 
DRAWN  WIRE  AT  DIFFERENT  LENGTHS  AT  70°F. 


Feet 

0 

10 

20 

30 

40 

50 

60 

70 

80 

90 

0 
100 
200 
300 
400 
500 

0.00998 
0.01996 
0.02994 
0.03992 
0.04990 

0.00099 
0.01097 
0.02095 
0.03093 
0.04091 
0.05089 

0.00199 
0.01197 
0.02195 
0.03193 
0.04191 
0.05189 

0.00299 
0.01297 
0.02295 
0.03293 
0.04291 
0.05289 

0.00399 
0.01397 
0.02395 
0.03393 
0.04391 
0.05389 

0.00499 
0.01497 
0.02495 
0.03493 
0.04491 
0.05489 

0.00598 
0.01596 
0.02594 
0.03592 
0.04590 
0.05588 

0.00698 
0.01696 
0.02694 
0.03692 
0.04690 
0.05688 

0.00798 
0.01796 
0.02794 
0.03792 
0.04790 
0.05788 

0.00898 
0.01896 
0.02894 
0.03892 
0.04890 
0.05888 

If  such  tables  are  not  at  hand,  as  in  the  case  of  work 
on  a  small  job  away  from  the  office,  one  can  obtain  the 
size  of  wire  required  by  remembering  that  1,000  ft.  of 
No.  10  B.  &  S.  gage  wire  has  a  resistance  of  approxi- 
mately 1  ohm  at  68°F.,  and  that  an  increase  of  three 
sizes  in  the  gage  number  divides  the  resistance  by  ap- 
proximately two,  and  vice  versa.  Thus  the  resistance 
of  No.  7  wire  is  half  that  of  the  same  length  of  No.  10 
wire,  and  the  resistance  of  No.  13  wire  is  double  that  of 
the  same  length  of  No.  10  wire. 

Consecutive  sizes  of  wire  differ  in  resistance  by  ap- 
proximately the  cube  root  of  2  (about  1.25);  that  is,, the 
resistance  of  a  definite  length  of  No.  11  wire  is  approxi- 
mately equal  to  one  and  a  quarter  times  the  resistance 
of  the  same  length  of  No.  10  wire,  and  the  resistance  of 
a  definite  length  of  No.  9  wire  is  approximately  equal 
to  the  resistance  of  the  same  length  of  No.  10  wire 
divided  by  1.25.  For  a  difference  in  gage  number  of 
two,  the  corresponding  factor  is  the  cube  root  of  4,  or 
1.58.  By  keeping  these  figures  in  mind  the  resistance 
of  any  length  of  any  size  of  wire  can  be  determined  with 
a  fair  degree  of  accuracy. 

In  a  three-wire,   direct-current  balanced  system  no 


WIRE  SIZES  FOR  D.  C.  CIRCUITS  49 

current  flows  in  the  middle  wire  if  a  true  balance  exists. 
For  such  a  system  the  size  of  the  wires  is  determined 
as  in  a  two- wire  system,  the  middle  wire  being  made  as 
large  as  the  outside  ones  for  safety,  although  some  engi- 
neers will  permit  the  middle  wire  to  be  made  smaller 
in  size. 

In  a  double-neutral  main,  the  object  of  which  is  to 
permit  the  use  of  either  a  two-wire  110-volt  D.-C.  system 
or  a  three- wire  110-220-volt  D.-C.  system,  the  circular 
millage  of  the  two  outside  wires  should  equal  the  cir- 
cular millage  of  the  middle  wire.  To  secure  this  result 
a  double-neutral  main  should  be  figured  for  loss  in 
pressure  as  if  it  was  a  two- wire  main  carrying  the 
required  current  at  110  volts. 

The  size  thus  obtained  would  be  the  size  of  the  middle 
or  double-neutral  wire  and  each  of  the  outside  wires 
should  have  one-half  of  the  circular  mils  of  the  neutral. 
For  example,  if  A  equals  the  circular  mils  of  each  wire, 
2A  would  be  the  total  circular  millage  of  a  two-wire 
main  carrying  current  at  110  volts.  In  a  three- wire 
double-neutral  main  the  circular  millage  of  each  wire 

would  be  ^  +  A  +  ~  =  2A. 

In  some  charts1  which  the  writer  has  seen  this  has  not 
been  adhered  to  and  instead  of  the  outside  wires  being 
half  of  the  neutral  wire  according  to  circular  mils,  the 
outside  wires  have  been  made  one-half  of  the  neutral 
wire  according  to  the  carrying  capacity  in  amperes  of 
the  neutral,  as  listed  in  the  National  Code. 

This  results  in  actual  practice  of  an  increased  loss  in 
pressure  (volts)  over  a  figured  one  and  under  some  con- 
ditions might  prove  embarrassing  to  a  contractor. 


1  National  Electric  Contractors  Association  Chart. 
4 


50 


THE  ELECTRICAL  CONTRACTOR 


Other  voltage  drops  must  be  taken  into  consideration 
in  addition  to  that  due  to  the  resistance  of  the  wire. 
Such  are  those  at  cut-outs,  panelboards  and  switches. 
On  main  circuits  an  allowance  of  0.1  volt  for  each  con- 
nection should  be  made,  while  on  branch  circuits  an 
allowance  of  0.1  volt  at  all  cut-outs  and  switches  should 
be  made. 

In  figuring  the  resistance  and  other  drops  in  branch 
circuits  the  same  method  is  employed  for  either  direct 


A 

t 

"°j  0.1-  Volt  Drop 
\j    at  Contact 

Distance=30ft. 
2.27  Amp.                   Distance=25  ft.  1.36  Amp. 

Or'                                     n             v 
X            l                                      2           X 
9  Four25-ft.                  Six  25-  Watt  9 
O       Lamps                           Lamps     V 

f 
.B\ 

~°\  0.1-  Volt  Loss                                                                    A 
^1  for  Contact 

Distance  =  50  ft. 
2.27  Amp. 

• 

FIG.  10. 

current  or  alternating  current.  The  voltage  drops  on 
branch  circuits  should  be  figured  separately  for  each 
length  of  circuit  between  outlets.  For  example,  in  the 
Fig.  10  is  the  panelboard  and  B  a  switch.  Ci  and  €2 
are  lamp  outlets.  A  two- wire  system  of  distribution  is  as- 
sumed and  the  distances  given  are  one-way  distances  only. 

At  Ci  there  are  four  25-watt  lamps  and  at  C2  there 
are  six  25-watt  lamps.  If  a  110-volt  system  is  installed, 
No.  14  wire  would  give  a  drop  of  1.29  volts,  as  follows: 

Resistance  of  No.  14  wire: 

AtoB  (100ft.)  =  0.2567 
B  to  Ci  (60  ft.)  =0.154 
Ci  to  C2  (50ft.)  =  0.1283 


WIRE  SIZES  FOR  D.  C.  CIRCUITS 


51 


By  Ohm's  law: 

0.2567  ohm  X  2.27  amp.  =  0.58  volt 
0.154  ohm  X  2.27  amp.  =  0.34  volt 
0.120  ohm  X  1.36  amp.  =  0.17  volt 
Total  line  resistance  drop  =  1 . 09  volts 
Assumed  loss  at  contact  A  =  0 . 1  volt 
Assumed  loss  at  contact  5  =  0.1  volt 
Total  drop  A  to  C  =  1.29  volts 

SIZE  OF  WIRE  FOR  GIVEN  VOLTAGE  DROP 

In  many  cases  it  is  necessary  to  know  what  size  of 
wire  will  be  required  with  a  definite  length  of  circuit  to 
give  a  certain  voltage  drop  with  a  certain  current.  Sup- 
pose, for  example,  that  it  is  necessary  to  transmit  elec- 
trical energy  a  distance  of  205  ft.  with  a  drop  of  2.5  volts, 
the  system  being  a  direct-current  110- volt  one,  the  cur- 
rent being  62  amp.,  and  the  205  ft.  being  single 
distance. 

For  a  drop  of  2.5  volts  and  a  current  of  62  amp.  the 
resistance  should  be  2.5  -f-  62,  or  0.0403  ohm.  If  tables 
are  at  hand  showing  the  resistances  required  with  differ- 
ent currents  to  give  various  voltage  drops,  this  calcula- 

TABLE  XXXI. — RESISTANCE  IN  OHMS  OP  ANY  CIRCUIT  CARRYING  A 
GIVEN  NUMBER  OF' AMPERES  WITH  A  DROP  OF  2.5  VOLTS 


Current 

0 

1 

2 

3 

4 

5 

6 

7 

8 

9 

0 

CO 

2  .  5000 

1  .  2500 

0.8333 

0  .  6250 

0.5000 

0.4166 

0.3571 

0.3125 

0.2778 

10 

0.2500 

0.2272 

0.2083 

0.1923 

0.1786 

0.1667 

0.1562 

0.1470 

0.1389 

0.1316 

20 

0.1250 

0.1190 

0.1136 

0.1087 

0.1042 

0.1000 

0.0961 

0.0962 

0.0892 

0.0862 

30 

0.0833 

0.0806 

0.0781 

0.0757 

0.0735 

0.0714 

0.0694 

0.0676 

0.0658 

0.0641 

40 

0.0625 

0.0609 

0.0595 

0.0581 

0.0568 

0.0555 

0.0543 

0.0532 

0.0521 

0.0510 

50 

0  .  0500 

0.0490 

0.0481 

0.0472 

0.0463 

0.0454 

0.0446 

0.0438 

0.0431 

0.0424 

60 

0.0417 

0.0410 

0.0403 

0.0397 

0.0391 

0.0384 

0.0379 

0.0373 

0.0368 

0.0362 

70 

0.0357 

0.0352 

0.0347 

0.0342 

0.0338 

0.0333 

0.0329 

0.0325 

0.0320 

0.0316 

80 

0.0312 

0.0309 

0.0305 

0.0301 

0.0297 

0.0294 

0.0291 

0.0287 

0.0284 

0.0281 

90 

0.0278 

0.0275 

0.0272 

0.0269 

0.0266 

0.0263 

0.026 

0.0258 

0.0255 

0.0252 

52  THE  ELECTRICAL  CONTRACTOR 

tion  is  unnecessary.  Such  tables,  where  used,  can  be 
made  in  the  form  shown  in  Table  XXXI.  This  table 
gives  resistance  required  for  2.5  volts  drop  for  currents 
of  0  amp.  to  99  amp.  in  steps  of  1  amp.  For  higher 
currents  one  should  remember  that  multiplying  the 
current  by  10  in  the  table  multiplies  the  resistance  values 
by  10.  This  table  could  have  been  applied  in  the  case 
given  by  following  the  horizontal  line  marked  60  and 
the  vertical  line  marked  2  (a  total  of  62  amp.)  until  they 
meet,  at  which  point  the  resistance  of  0.0403  ohm  is 
obtained.  After  the  ohmic  resistance  is  found — namely, 
0.0403  ohm — one  can  find  the  corresponding  size  of 
wire — namely,  No.  0 — by  means  of  tables  such  as  Table 
XXX,  or  by  means  of  the  relation  existing  between  sizes 
of  wire. 


CHAPTER  VI 

CALCULATING  WIRE  SIZES  FOR  ALTERNATING- 
CURRENT   CIRCUITS 

In  figuring  the  voltage  drop  in  alternating-current 
circuits  there  are  a  number  of  voltage  losses  to  be  taken 
into  consideration  in  addition  to  the  resistance  drop — 
namely,  skin  effect,  inductance  and  capacity.  The  skin 
effect  is  very  small  unless  the  size  of  the  wires  is  excess- 
ive. The  other  losses  may  be  considerable.  The 
writer  has  worked  out  multiplying  factors  which,  when 
applied  to  the  cross-section  of  wires  as  figured  for  re- 
sistance drop,  give  fairly  accurate  values  for  the  total 
voltage  drop  in  alternating-current  circuits,  provided 
that  all  the  wires  of  the  circuit  are  placed  in  the  same 
conduit. 

Before  considering  the  subject  of  voltage  drop,  how- 
ever, it  is  best  to  discuss  the  subject  of  power-factor. 
The  power-factor  of  a  generator,  motor  or  complete 
wiring  system  is  the  ratio  of  the  actual  power  required 
to  the  apparent  power  required,  or  it  is  the  ratio  of  the 
power  required  as  measured  on  a  wattmeter  to  the  prod- 
uct of  the  voltage  and  current  as  measured  on  a  volt- 
meter and  an  ammeter.  For  example,  a  20-hp.  motor 
theoretically  should  consume  at  full  load  20  X  746,  or 
14,920  watts.  When  the  voltage  and  current  at  full 
load  are  actually  measured,  it  may  be  found  that  their 
product  is  18,660  watts,  in  which  case  the  power-factor 
would  be  14,920  -r-  18,660,  or  80  per  cent.  In  other 

53 


54  THE  ELECTRICAL  CONTRACTOR 

words,  to  obtain  the  volt-ampere  intake  of  an  alternating- 
.current  motor,  divide  the  rating  of  the  motor  in  watts 
by  the  power-factor  in  per  cent,  and  multiply  by  100. 
Divide  this  result  by  the  voltage,  and  the  result  is  the 
current  required  in  amperes. 

The  power-factor  of  a  circuit  varies  with  the  types 
of  the  loads  connected,  the  values  given  in  Table  XXXII 
being  what  the  United  States  Treasury  Department 
gives  as  fair  averages. 

TABLE  XXXII. — AVERAGE  POWER-FACTORS  FOR  LIGHT  AND  POWER  IN 

PER  CENT. 

Incandescent  lamps 95 

Arc  lamps 70 

Incandescent  lamps  and  induction  motors  on  same  circuit  .   85 

Induction  motors,  full  load 80 

Induction  motors,  constant-speed  type,  starting 60 

Induction  motors,  elevator-type,  starting 40 

The  writer  has  found  that  a  good  method  for  finding 
the  sizes  of  wire  required  in  an  alternating-current  sys- 
tem for  a  given  voltage  drop  where  all  wires  of  the 
circuit  are  run  in  the  same  conduit  is  first  to  base 
the  calculation  on  a  two-wire  direct-current  system  at  the 
same  voltage,  including,  of  course,  the  power-factor  in 
calculating  the  current.  For  example,  consider  the  cal- 
culations for  a  two-phase,  220-volt,  four-wire  main  feed- 
ing a  50-hp.  motor.  The  length  of  the  run  is  200  ft., 
the  voltage  drop  is  to  be  2.2  volts,  or  1  per  cent.,  and  the 
power-factor  is  80  per  cent. 

Rating  of  motor  in  watts  =  50  X  746  =  37,300  watts. 

Current  without  power-factor  allowance  =  37,300  4- 
220  =  169.5  amp. 

Current  with  power-factor  allowance  =  (169.5  -f-  80) 
X  100  =  211.9  amp. 

The  resistance  that  would  be  required  in  a  two-wire 


WIRE  SIZES  FOR  A.  C.  CIRCUITS 


55 


direct-current  circuit  to  give  a  drop  of  2.2  volts  with  a 
current  of  211.9  amp.  would  be  2.2  -=-  211.9  or  0.01  ohm. 

A  wire  having  a  resistance  of  0.01  ohm  for  200  ft.  of 
circuit  or  400  ft.  of  wire  would  have  a  cross-sectional 
area  of  about  400,000  circ.  mils. 

The  next  step  would  be  to  find  the  size  of  wire  based 
on  a  two-phase,  four-wire  system  at  the  same  voltage 
and  having  the  same  percentage  of  voltage  drop.  Table 
XXXIII  shows  the  relative  sizes  of  wires  for  all  systems 
when  carrying  the  same  load  at  the  same  percentage 
of  voltage  drop. 

TABLE  XXXIII. — RELATIVE  SIZES  OF  WIRES  FOR  SAME  LOAD  AND  PER- 
CENTAGE VOLTAGE  DROP 


Volts 

No.  of 
wires 

No.  of 
phases 

Kind  of 
energy 

Cross-section  of  wires 

Total  cross-section 

110 

2 

B.C. 

A;  A 

2A 

110 

2 

1 

A.C. 

A;  A 

2A 

220 

2 

D.C. 

A/4;  A/4 

0.5A 

220 

2 

1 

A.C. 

A/4;  A/4 

0.5A 

110-220 

3 

D.C. 

A/4;  A/4;  A/4 

0.75A 

110 

4 

2 

A.C. 

A/2;  A/2;  A/2;  A/2 

2A 

110 

3 

2 

A.C. 

A/2;  1.4A/2;  A/2 

1.7A 

220 

4 

2 

A.C. 

A/8;  A/8;  A/8;  A/8 

0.5A 

Plus  increase 

for  inductive 

220 

3 

2 

A.C. 

A/8;  1.4A/8;  A/8 

0.425A 

reactance 

110 

3 

3 

A.C. 

A/2;  A/2;  A/2 

1.5A 

drop 

220 

3 

3 

A.C. 

A/8;  A/8;  A/8 

0.375A 

In  the  example  given  it  was  found  that  for  a  two- 
wire,  direct-current,  220-volt,  50-hp.  motor  a  conductor 
having  a  cross-section  of  400,000  circ.  mils  would  be 
required.  For  a  two-phase,  220-volt,  four-wire  system 
the  size  of  wires  per  leg  would  be  one-half  of  this  size, 
or  200,000  circ.  mils.  This  cross-section  of  200,000 
circ.  mils  corresponds  approximately  to  a  No.  0000  B. 
&  S.  gage  conductor.  However,  the  cross-section  must 
be  increased  to  take  care  of  the  inductive  reactance  drop. 


56 


THE  ELECTRICAL  CONTRACTOR 


For  estimating  purposes  the  writer  has  prepared 
Table  XXXIV  of  multiplying  factors  for  use  in  com- 
puting sixty-cycle  alternating-current  circuits.  Multi- 
plying the  cross-sectional  area  of  a  conductor  as  found 
above  by  the  factor  given  in  the  table,  the  approximately 
correct  size  of  rubber-covered  wire  will  be  obtained, 
provided  that  all  wires  of  one  circuit  are  run  in  the  same 
conduit. 

TABLE  XXXIV. — MULTIPLYING  FACTORS  FOR  SIXTY-CYCLE,  TWO-PHASE 
AND  THREE-PHASE  ALTERNATING-CURRENT  CiRcuiTS1 


Size  of  wire  as  calculated 

Cross-section  re- 
quired in  circ.  mils 

Nearest  commercial 
size  to  that  required 

Gage  No.,  B.  &  S. 

Circ.  mils 

Multiplier 

14 

4,107 

.00 

4,107 

14 

12 

6,530 

.00 

6,530 

12 

10 

10,380 

.00 

10,380 

10 

8 

16,510 

.00 

16,510 

8 

6 

26,250 

.00 

26,250 

6 

5 

33,100 

.01 

33,431 

5 

4 

41,740 

.02 

42,575 

4 

3 

52,630 

.03 

54,209 

3 

2 

66,370 

.06 

70,352 

1 

1 

83,690 

1.09 

91,222 

0 

0 

105,500 

1.12 

118,160 

00 

00 

133,100 

1.21 

161,051 

000 

000 

167,800 

1.32 

221,496 

225,000 

0000 

211,600 

1.47 

311,052 

300,000 

250,000 

1.62 

405,000 

400,000 

300,000 

1.82 

546,000 

550,000 

350,000 

2.06 

721,000 

750,000 

400,000 

2.28 

912,000 

950,000 

450,000 

2.53 

1,138,500 

1,200,000 

500,000 

2.86 

1,430,000 

1,500,000 

1  These  figures  are  based  on  rubber-covered  wires  run  in  conduit,  all 
wires  of  one  circuit  being  run  in  the  same  conduit.  They  should,  hence, 
only  be  used  where  these  conditions  exist. 


WIRE  SIZES  FOR  A.  C.  CIRCUITS 


57 


The  size  of  wire  which  would  have  been  required  for 
a  direct-current  system  was  found  to  be  of  200,000-circ. 
mil  cross-section.  The  multiplier  in  this  case  as  found 
in  Table  XXXIV  is  1.47.  Hence  200,000  X  1.47  = 
294,000  circ.  mil,  the  nearest  commercial  size  being  a 
300,000-circ.  mil  wire. 

Before  deciding  that  a  300,000-circ.  mil  wire  is  the 
proper  size  to  use,  it  should  be  checked  for  carrying 
capacity.  Table  XXXV  gives  the  current  required  by 
alternating-current  motors  per  horsepower  per  phase 
for  different  voltages,  the  effect  of  power-factor  being 
taken  into  consideration.  The  values  given  have  been 
found  to  be  fair  averages  for  all  types  of  alternating- 
current  motors. 

TABLE    XXXV. — CURRENT   CONSUMPTION   OF   ALTERNATING-CURRENT 

MOTORS1 


Motor 

Amperes  per  hp.  per  phase 

Phases 

Volts 

1 

110 

10.0 

1 

220 

5.0 

2 

110 

5.0 

2 

220 

2.5 

3 

110 

5.6 

3 

220 

2.8 

1  When  starting  without  load  the  currents  given  in  the  table  should 
be  multiplied  by  1.4,  and  when  starting  at  full  load  the  values  should  be 
multiplied  by  1 . 8. 

It  was  found  that  a  300,000-circ.  mil  wire  was  the 
proper  size  for  taking  care  of  the  voltage  drop.  The 
starting  currents  are: 

(50  X  2.5)  X  1.4  =  175  at  no  load 
(50  X  2.5)  X  1.8  =  225  at  full  load 


58  THE  ELECTRICAL  CONTRACTOR 

In  both  cases  the  current  is  below  the  allowable  carry- 
ing capacity  of  a  300,000-circ.  mil  cable,  namely,  275 
amp.  Hence  it  is  safe  to  use  cables  of  this  cross- 
section. 

CALCULATION  OF  VOLTAGE  DROP  IN  OVERHEAD  LINES 

In  dealing  with  overhead-construction  problems  it 
must  be  remembered  that  the  line  drop  is  due  to  two 
factors — first,  to  ohmic  resistance,  and  second,  to  the 
reactance  of  the  line  caused  by  self-induction.  The  cur- 
rent which  will  flow  under  such  conditions  is  expressed 
by  the  formula: 

/=        E 


In  this  formula  /  is  the  current  in  amperes,  E  the 
voltage  drop,  R  the  resistance  of  the  circuit  in  ohms,  / 
the  frequency  in  cycles  per  second,  and  L  the  self- 
induction  of  the  circuit  expressed  in  henries. 

The  value  of  L — that  is,  the  self-induction  of  the  cir- 
cuit— can  be  accurately  and  simply  determined  for  the 
case  of  a  circuit  where  the  outgoing  and  returning  wires 
are  parallel  and  no  iron  is  near.  These  conditions  exist 
in  most  overhead  lines. 

If  I  be  the  total  wire  length  of  a  two-wire  circuit  in 
feet,  d  the  distance  between  the  axes  of  the  two  wires, 
and  r  the  radius  of  the  bare  wires  expressed  in  the  same 
units  as  d,  then  the  self-inductance  L  of  the  circuit  in 
henries  is  expressed  by  the  formula : 

30.48Z[0.5  +  4.6052  log  d/r] 
L  =  1,000,000,000 


WIRE  SIZES  FOR  A.  C.  CIRCUITS 


59 


The  factor  2irfL  is  known  as  the  reactance  of  the 
circuit. 

To  calculate  the  total  voltage  drop  resulting  from  the 
reactance  drop  plus  the  resistance  drop,  the  two  must 
be  combined  at  right  angles  as  shown  in  Fig.  li- 
the hypotenuse  of  the  triangle  will  then  represent  the 
impedance  drop,  that  is,  the  total  drop  in  voltage  along 
the  line. 

For  example,  take  a  line  1,000  ft.  long  consisting  of 
two  No.  0  copper  wires  so  strung  that  the  distance  be- 


Reactance  Drop=27r/iJ 
FlG.    11. 


tween  the  centers  of  the  wires  is  12  in.  What  will  be 
the  voltage  drop  if  the  value  of  the  alternating  current 
is  10  amp.  and  its  frequency  is  125  cycles  per  second? 

The  inductance  in  henries  is  found  by  the  formula 
previously  given : 

_  30.48  X  2,000  [0.5  +  4.6052  log  12/0.19] 

1,000,000,000 
=  0.00056  henry. 


60  THE  ELECTRICAL  CONTRACTOR 

The  resistance  of  2,000  ft.  of  No.  0  wire  is  0.1996  ohm. 
The  impedance  Z  then  becomes 


Z  =      #2  +  (27T/L) 


=  Vo.19962  +  (2  X  3.1416  X  125  X  0.00056)2 
=  0.48  ohm. 

The  voltage  drop  is  E  =  IZ  =  10  X  0.48,  or  4.8  volts. 
The  voltage  drop  due  to  resistance,  on  the  other  hand, 
is  only  10  X  0.1996,  or  1.996  volts. 

Suppose  that  the  allowable  drop  in  volts  is  specified 
in  the  case  of  a  three-phase,  three-wire  transmission 
line  with  the  wires  placed  at  the  corners  of  an  equilateral 
triangle  and  that  the  size  of  the  wires  must  be  deter- 
mined. Let  300  kw.  be  the  energy  to  be  transmitted, 
the  frequency  being  sixty  cycles  per  second,  the  pressure 
1,200  volts,  and  the  voltage  drop  5  per  cent.,  the  wires 
being  24  in.  apart  between  centers,  and  the  length  of  the 
line  (single-  wire  distance)  1,800  ft. 

300,000 

Current  per  phase  =  -         —  p  =  145  amp. 
1,200  V3 

If  the  line  were  a  single-phase  circuit,  the  current 
would  be  250  amp.  To  calculate  the  loss  in  the  case 
of  a  three-phase  feeder,  consider  each  conductor  as 
carrying  125  amp.  (that  is,  one-half  of  the  correspond- 
ing single-phase  current)  and  complete  the  calculations 
as  in  the  case  of  a  single-phase  line. 

Volts  drop  =  0.05  X  1,200  =  60  volts. 
Double  distance  =  3,600  ft. 

30.48?  (0.5  +  4.6053  log  d/r) 
1,000,000,000  ~ 


WIRE  SIZES  FOR  A.  C.  CIRCUITS  61 

At  this  point  it  is  necessary  to  assume  a  value  for  r; 
that  is,  the  radius  of  the  conductor.  Let  0.3  in.  be  as- 
sumed, this  being  the  approximate  radius  of  a  300,000- 
circ.  mil  cable.  The  log  d/r  does  not  change  appreciably 
with  slight  changes  in  r  owing  to  the  relatively  great 
value  of  d,  and  hence  great  accuracy  is  unnecessary. 

_  30.48  X  3,600(0.5  +  4.6052  log  24/0.3) 

L  =  1,000,000,000 


Impedance  =  \2  +  (27T/L)2  = 
V0.1262  +  (2  X  3.1416  X  60  X  0.001)2  =  0.39  ohm. 

Now  0.126  ohm  is  the  ohmic  resistance  of  3,600  ft.  of 
300,000-circ.  mil  cable. 


/  X      #2  +  (27T/L)2  =  E, 
or  125  amp.  X  0.39  =  48  volts. 

As  60  volts  drop  is  permissible  and  a  300,000-circ. 
mil  cable  gives  only  48  volts  drop,  a  No.  0000  wire  will 
be  found  to  be  approximately  correct  for  a  drop  of  60 
volts. 


CHAPTER  VII 
ILLUMINATION  CALCULATIONS 

A  great  many  contractors  merely  " guess  at"  the 
number  of  lamps  required  in  the  average  installation. 
As  a  result,  it  often  happens  that  either  too  few  or  too 
many  are  installed.  In  either  event  the  customer  is 
dissatisfied.  In  the  first  case  he  does  not  obtain  the 
good  illumination  desired,  while  in  the  second  case  his 
lighting  bill  is  excessive  if  all  the  lamps  are  used.  The 
customer  can,  of  course,  change  the  size  of  the  lighting 
units,  but  this  should  not  be  necessary. 

Recently,  however,  there  has  been  an  improvement  in 
this  respect  as  the  result  of  the  educational  campaigns 
that  have  been  conducted  by  lamp  and  reflector  manu- 
facturers. Several  comparatively  easy  and  satisfactory 
methods  have  been  devised  for  calculating  the  number 
of  lamps  required  in  the  average  installation. 

DEFINITION  OF  TERMS 

In  order  to  be  able  to  solve  illumination  problems  the 
contractor  should  make  himself  familiar  with  the  fol- 
lowing terms  and  their  definitions: 

The  candlepower  is  the  unit  of  light  production  and 
is  defined  as  the  light  from  a  standard  international 
candle  burning  under  exact  specifications.  When  a 
source  of  light  is  spoken  of  as  being  a  16  cp.,  it  is  meant 
that  its  intensity  equals  that  of  sixteen  international 

62 


ILLUMINATION  CALCULATIONS  63 

candles.  In  general,  however,  the  candlepower  of  a 
source  of  light  is  not  the  same  in  all  directions. 

The  foot-candle  is  the  unit  of  intensity  of  illumina- 
tion. As  such  it  is  the  intensity  of  illumination  pro- 
duced by  a  1-cp.  source  on  a  surface  1  ft.  from  the  source 
and  perpendicular  to  the  direction  of  the  light.  The 
intensity  of  illumination  of  a  unit  surface  perpendicular 
to  the  beam  of  light  incident  upon  it  is  directly  propor- 
tional to  the  candlepower  of  the  source  of  light  and 
inversely  proportional  to  the  square  of  the  distance  of  the 
point  from  the  source. 

Calling  7  the  intensity  of  illumination,  in  foot-candles, 
of  a  unit  surface  perpendicular  to  the  rays  of  light  inci- 
dent upon  it,  c  the  candlepower  of  the  source,  and  d 
the  distance  in  feet  from  the  surface  to  the  source  of 
light,  the  following  formula  is  obtained:  7  =  c/d2. 


Rays  of  Light 

D                 B 

\                 / 

\                           / 

/ 

1           j 

I                                 SiZ/ 

i  / 

i/ 

A 

FIG.  12. — Intensity  of  illumination  on  an  inclined  surface. 

Now,  if  the  surface  is  not  perpendicular  to  the  beam 
of  light  incident  upon  it,  as  is  the  case  with  the  surface 
represented  by  the  dotted  line  AD  in  Fig.  12,  but  at  an 
angle  to  it,  such  as  the  surface  represented  by  A  B,  the 
intensity  of  illumination  is  reduce^.  A  glance  at  the 
figure  will  show  how  this  is  true,  for  in  the  case  of  the 
surface  AB  the  same  number'  of  light  rays  are  dis- 


64,  THE  ELECTRICAL  CONTRACTOR 

tributed  over  the  surface  as  over  the  smaller  surface 
AD.  Hence  the  intensity  of  illumination  of  the  surface 
AB  compared  with  the  intensity  on  a  surface  at  right 
angles  to  the  rays  of  light  is  in  the  ratio  of  the  length 
of  the  line  AD  divided  by  the  length  of  the  line  AB. 
This  relation  may  also  be  expressed  by  the  formula  in 
which  the  resulting  intensity  7  =  c/d2  cos  <p,  where  the 
angle  <p  is  the  angle  between  the  surface  A B  and  a  sur- 
face AD  perpendicular  to  the  rays  of  light  incident 
upon  AB.  The  expression  cos  $  is  simply  a  mathe- 
matical way  of  indicating  the  ratio  of  the  lengths 
AD  -=-  AB. 

These  formulas,  of  course,  assume  that  all  rays  of 
light  incident  upon  the  surface  come  directly  from  the 
one  source  considered,  and  that  no  reflection  from  walls, 
etc.,  takes  place.  It  is  also  assumed  that  the  surface 
under  consideration  is  small  enough  and  situated  at  a 
great  enough  distance  from  the  source  of  light  to  justify 
the  assumption  that  the  rays  of  light  incident  upon  it 
are  practically  parallel. 

CANDLEPOWER  CURVES 

Before  considering  the  calculation  of  the  number  and 
spacing  of  lamps  required  for  proper  illumination  of 
rooms  devoted  to  various  purposes  it  is  best  to  study 
the  distribution  of  light  in  the  case  of  the  common 
tungsten-filament  lamp  with  and  without  an  extensive 
type  of  reflector.  Fig.  13  shows  candlepower  measure- 
ments taken  of  a  40-watt  tungsten-filament  lamp  at 
various  angles,  both  with  (curve  B)  and  without  (curve 
A)  an  extensive- type  Holophane  reflector.  The  lamp  is 
assumed  to  be  at  the  center  of  the  concentric  circles  in 


ILLUMINATION  CALCULATIONS 


65 


such  a  position  that  the  tip  of  the  glass  bulb  points 
downward  to  what  corresponds  to  the  bottom  edge  of 
the  page.  Readings  were  taken  at  every  15  deg.  in  a 
plane  passing  through  the  glass  stem  supporting  the 
filament  of  the  lamp. 

It  will  be  noticed  from  curve  A  that  a  bare  tungsten- 
filament  lamp  has  its  maximum  candlepower  intensity 


FIG.   13. — Candle-power  curves  for  40-watt  tungsten  type  B  lamp  with 
and  without  extensive  reflector. 


in  a  horizontal  direction.  Directly  beneath  the  lamp 
the  candlepower  is  very  low.  The  zero  reading  at  the 
top  of  the  lamp  is,  of  course,  due  to  the  fact  that  the 
base  of  the  lamp  intercepts  all  light  in  that  direction. 

Curve  B  shows  the  distribution  when  an  extensive 
type  of  Holophane  reflector  is  used.  The  curve  clearly 
shows  that  such  a  reflector  causes  a  more  desirable  dis- 
tribution of  the  rays  of  light  from  the  lamp. 


66  THE  ELECTRICAL  CONTRACTOR 

INTENSITY  OF  ILLUMINATION 

In  Fig.  14  is  given  a  diagram  of  a  room  illuminated 
by  means  of  a  40- watt  tungsten-filament  lamp  placed  in 
the  center  of  the  ceiling  and  equipped  with  an  extensive- 
type  reflector.  This  diagram  will  be  used  to  illustrate 
some  of  the  principles  heretofore  discussed. 

Let  it  be  required  to  find  the  intensity  of  illumination 
on  the  unit  areas  A  and  B  of  the  two  tables  indicated, 
the  effect  of  reflection  from  all  surfaces  being  neglected. 

From  the  curve  in  Fig.  13  it  is  found  that  the  ver- 
tically downward  candlepower  of  the  40-watt  lamp  with 
an  extensive  type  of  reflector  is  28  cp.  Now  the  dis- 
tance from  the  center  of  the  lamp  to  the  surface  of  the 
table  at  A  is  8  ft.,  the  surface  of  the  table  being  as- 
sumed to  be  2.5  ft.  above  the  floor  level.  In  most  illumi- 
nation problems  it  is  generally  assumed  that  the  plane 
of  illumination  is  at  this  distance  above  the  floor,  since 
the  surfaces  of  tables,  desks,  etc.,  average  about  this 
height.  The  point  A  is  assumed  to  be  directly  beneath 
the  center  of  the  incandescent  lamp  above,  and  hence 
the  rays  incident  upon  a  small  area  at  A  will  be  prac- 
tically perpendicular.  Hence  the  following  formula 
applies : 

/  =  c/d*  =  28  -5-  (8  X  8)  =  0.438  ft.-candle. 

Now,  let  it  be  required  to  find  the  intensity  of  illumi- 
nation at  a  unit  surface  B  on  the  table  shown  at  the 
right  in  Fig.  14.  In  this  case  the  point  considered,  B, 
is  8  ft.  below  the  lamp  and  8  ft.  to  the  right.  Hence  the 
distance  y  is  about  11.3  ft. 

=  \/64  +  64  =  Vl28  =  11.3). 


ILLUMINATION  CALCULATIONS 


67 


Referring  to  Fig.  13,  it  is  seen  that  the  candlepower 
of  the  lamp  at  an  angle  of  45  deg.  below  the  horizontal 
is  approximately  47  cp. 

As  the  rays  of  light  y  strike  B  at  an  angle  of  45  deg., 
the  formula  applies: 

/  =  c/d2  cos  <?  =  47  -r-  128  cos  <p 

=  (47  ^  128)  X  0.707  =  0.26  ft.-candle. 

In  the  same  manner  the  intensity  of  illumination  at 
any  point  in  the  room  may  be  obtained. 


FIG.  14. — Illumination  from  ceiling  fixture. 

The  intensity  of  illumination  at  any  point  in  a  room, 
however,  depends  also  upon  other  factors  which  as  yet 
have  not  been  taken  into  consideration.  The  most  im- 
portant of  these  is  the  effect  produced  by  the  reflection 
of  light  from  walls,  ceilings,  etc.  In  Table  XXXVI  are 
given  the  percentage  correction  factors  which  should  be 
applied  to  results  obtained  as  previously  described  in 
order  to  obtain  a  more  accurate  estimate  of  the  inten- 


68 


THE  ELECTRICAL  CONTRACTOR 


sity  of  illumination  at  any  point.  This  table  and  all 
others  in  this  installment  are  based  on  data  furnished 
by  manufacturers  of  lamps,  shades  and  reflectors.  It  is 
thus  seen  that  the  results  previously  obtained  should  be 
increased  by  from  0  to  80  per  cent.,  depending  upon 
the  condition  of  the  walls  and  ceilings. 

CALCULATION  OF  THE  SIZE  OF  UNITS 

A  reversal  of  the  process  outlined  will  permit  calcu- 
lation of  the  size  of  lighting  units  to  be  installed  in 
order  to  produce  a  certain  intensity  of  illumination  at 
given  points. 

Let  it  be  assumed  that  an  intensity  of  illumination 
of  0.3  ft.-candle  is  desired  at  A  in  Fig.  14,  the  room 
having  ceiling  and  walls  of  medium  color.  From  Table 
XXXVI  it  is  seen  that  the  effect  of  the  reflection  from 
ceilings  and  walls  is  to  increase  the  average  illumination 
about  40  per  cent.  Hence  0.3  ft.-candle  respresents 
140  per  cent,  of  the  intensity  of  illumination  due  to 
direct  light  from  the  lamp  above,  and  the  rays  of  the 
lamp  must  provide  an  intensity  of  illumination  at  A  of 
0.3  -T-  1.40  ft.-candles,  or  0.214  ft.-candle.  Since  from 
the  formula  already  given,  c  =  Id2,  substituting, 

C  =  0.214  X  64  =  13.7  cp. 

TABLE  XXXVI. — EFFECT  OF  NATURE  OF  WALLS  ON  ILLUMINATION 


Color  of  ceiling 

Color  of  walls 

Increase  of  calculated 
illumination,  per  cent. 

Very  dark 

Very  dark 

0 

Medium 

Very  dark 

15 

Medium 

Medium 

40 

Very  light 

Very  dark 

30 

Very  light 

Medium 

55 

Very  light 

Very  light 

80 

ILLUMINATION  CALCULATIONS 


69 


TABLE  XXXVII. — ABSORPTION  OF  LIGHT  BY  GLOBES 

Material  Percentage 

Clear  glass 5  to  12 

Light  sand-blasted  glass 10  to  20 

Albaster  glass 10  to  30 

Canary -colored  glass 10  to  20 

Opaline  glass 15  to  40 

Ground  glass 20  to  30 

Medium  opalescent  glass 20  to  40 

Opal  glass 25  to  60 

Heavy  opalescent  glass 30  to  50 

Milk  glass 30  to  60 

Signal-green  glass 80  to  90 

Light-green  glass 30  to  40 

Ruby  glass 85  to  90 

Cobalt-blue  glass 90  to  95 

TABLE  XXXVIII. — DESIRABLE  SIZES  OF  SQUARES  FOR  SPACING  OUTLETS 


Ceiling  height 

Desirable  length 
of  sides  of  squares 

Armories 

12  ft.  to  16  ft. 

12  ft.  to  16  ft 

Auditoriums 

12  ft.  to  16  ft. 

12  ft  to  16  ft 

Public  halls  
Rinks  

Over  16  ft. 
Over  16  ft. 

15  ft.  to  26  ft. 
15  ft.  to  26  ft. 

Stores 

8  ft  to  11  ft 

8  ft  to  11  ft 

Stores  
Stores  

11  ft.  to  15  ft. 
Over  15  ft. 

10  ft.  to  16  ft. 
14  ft.  to  22  ft. 

Offices  with  individual  desk  lamps  
Offices  without  individual  desk  lamps.  .  . 
Offices  without  individual  desk  lamps.  .  . 
Offices  without  individual  desk  lamps.  .  . 

10  ft.  to  20  ft. 
9  ft.  to  12  ft. 
12  ft.  to  16  ft. 
Over  16  ft. 

12  ft.  to  18  ft. 
7  ft.  to  11  ft. 
9  ft.  to  14  ft. 
11  ft.  to  18ft. 

To  find  the  size  of  lamp  required  it  would  be  neces- 
sary to  have  curves  of  distribution  of  candlepower  of 
numerous  sizes  of  lamps  equipped  with  various  shades 
and  reflectors  at  hand.  The  lamp  and  reflector  or  shade 
arrangement  which  shows  a  candlepower  of  13.7  in  a 
downward  direction  would  be  selected  if  other  conditions 
were  not  to  be  taken  into  account. 


70  THE  ELECTRICAL  CONTRACTOR 

However,  in  most  illuminating  problems  it  is  neces- 
sary to  fulfill  specifications  for  intensity  of  illumina- 
tion at  more  than  one  point  in  the  room. 

By  applying  the  method  outlined  for  various  points  in  a 
room  it  is,  of  course,  possible  to  find  the  combination 
of  lamps  and  reflectors  that  will  approximately  fulfill  the 
required  conditions.  This  method  of  calculation,  how- 
ever, requires  the  plotting  of  curves  showing  the  dis- 
tribution of  light  for  numerous  sizes  of  lamps  with 
various  types  of  shades  and  reflectors.  The  method 
can  be  applied  to  rooms  in  which  only  one  unit  is  re- 
quired, but  when  extended  to  several  rooms  where  more 
than  one  lighting  unit  is  to  be  installed  it  becomes  very 
laborious.  Hence  recourse  is  generally  had  to  another 
method  of  calculating  the  size  of  lighting  units  required. 

THE  FLUX-OF-LIGHT  METHOD 

The  flux-of-light  method  is  based  upon  the  idea  of 
luminous  flux;  that  is,  luminous  energy  proceeding  from 
the  source  into  space  in  all  directions.  Consider  a  lamp 
placed  at  the  center  of  a  sphere  of  unit  radius  so  that 
one  unit  of  area  of  this  sphere  may  represent  one  unit 
of  solid  angle,  then  a  lamp  giving  an  intensity  of  illumi- 
nation of  1  cp.  in  every  direction  will  cause  a  certain 
amount  of  light  or  light  flux  to  pass  through  a  unit 
cone;  that  is,  through  an  area  of  unit  size  on  the  surface 
of  the  sphere.  This  unit  of  light  flux  is  called  a  lumen 
of  light  flux.  In  other  words,  the  lumen  is  the  quantity 
of  light  falling  on  1  sq.  ft.  of  a  sphere  of  1-ft.  radius 
from  a  light  source  of  1-cp.  intensity  at  the  center  of 
the  sphere. 


ILLUMINATION  CALCULATIONS  71 

TABLE  XXXIX. — INTENSITIES  OF  ILLUMINATION  FOUND  SUITABLE  FOR 
VARIOUS  PURPOSES 

Installation  Foot-candles 

Auditoriums 1  to    3 

Theaters,  general  illumination 1  to    3 

Churches,  general  illumination 2  to    3 

Reading  rooms 1  to    3 

Residences,  general  illumination 1  to    2 

Desk  illumination 2  to    5 

Postal  service 2  to    5 

Bookkeeping 3  to    5 

Stores,  general 2  to    5 

Stores,  clothing 4  to    7 

Drafting 5  to  10 

Engraving 5  to  10 

TABLE  XL. — EFFECTIVE  LUMENS  PER  LAMPX 
Tungsten  type  C  lamps.     Watts  per  lamp 

100    200     300     400     500     750      1000 
Effective  lumens  per  lamp 650  1440  2360  3140  4140  6530  10000 

Tungsten  type  B  lamps.     Watts  per  lamp 

25      40       60      100     150       250 
Effective  lumens  per  lamp 120     200     310     525     785     1360 

1  The  table  above  shows  the  lumens  effective  for  ordinary  lighting 
with  ''Mazda"  lamps  and  clear  high-efficiency  reflectors  in  rooms  with 
average  or  dark  walls  and  ceiling. 

This  method  is  generally  applied  in  the  shape  of  the 
following  formula: 

AT       u        .1  Sxl 

Number  of  lamps  =  —& — rr — , —  — \ —  — > 

effective  lumens  per  lamp 

where  S  =  the  number  of  square  feet  floor  area  of  the 
room  and  7  =  the  required  average  intensity  of  illumi- 
nation required  in  foot-candles.  The  term  "  effective 
lumens  per  lamp"  refers  to  the  total  light  flux  from 
lamps  that  is  available  for  illumination  purposes. 

To  illustrate  this  method  the  following  examples  may 
be  cited.  A  storeroom  to  be  lighted  measures  40  ft.  by 
100  ft.  Considering  the  goods  to  be  sold,  it  is  decided, 


72  THE  ELECTRICAL  CONTRACTOR 

after  referring  to  the  table  of  foot-candle  intensities 
recommended  for  various  classes  of  service  (Table 
XXXIX),  that  3  ft.-candles  is  sufficient  for  general 
illumination.  Then  the  total  lumens  of  light  flux  re- 
quired would  be  three  times  the  area  in  square  feet,  or 
40  X  100  X  3,  which  is  equal  to  12,000  lumens.  By 
turning  to  Table  XL  of  effective  lumens  for  tungsten- 
filament  lamps  it  is  found  that  under  ordinary  conditions 
the  number  of  25-watt,  type  B  lamps  necessary  would 
be  12,000  -5-  120,  or  100.  With  40-watt  lamps  12,000 
-T-  200,  or  60,  would  be  required. 

These  calculations  are  subject  to  correction  for  color 
of  the  wall  and  ceilings,  types  of  reflectors  used,  etc. 
For  example,  if  clear  holophane  reflectors  are  to  be  used 
in  the  store  referred  to  above,  and  the  walls  and  ceiling 
are  of  medium  tint,  the  effective  lumens  from  the  lamps 
may  be  considered  as  10  per  cent,  greater.  If  opaque 
reflectors  were  used  instead  of  clear  glass,  the  increase 
in  illumination  resulting  from  light  ceilings  and  walls 
would  be  negligible,  while  if  certain  kinds  of  opal  glass 
shades  were  used  the  influence  of  color  of  the  ceiling 
and  walls  would  be  greater.  It  is  somewhat  difficult  to 
estimate  the  difference  in  resulting  illumination  with 
different  color  decorations,  and  in  residence  work,  where 
the  wall  paper  may  be  changed  from  time  to  time,  it  is 
not  wise  to  rely  too  much  on  reflection  from  surfaces. 

For  lighting  by  the  use  of  indirect-lighting  fixtures 
the  writer  has  found  the  flux-of-light  method  to  be 
very  satisfactory  when  based  on  0.4  watt  per  foot- 
candle  for  each  square  foot  of  horizontal  surface  to  be 
illuminated. 

To  find  the  proper  type  of  reflectors  to  be  used  curves 
like  those  shown  in  Fig.  15  may  be  employed.  To  find 


ILLUMINATION  CALCULATIONS 


73 


the  proper  shade  to  be  used,  knowing  the  height  of  the 
unit  above  the  floor  level  and  the  spacing  between  units, 
follow  the  vertical  line  representing  the  spacing  between 


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10    12    14    16    18    20    22    24    26    28   30    32   34 
Spacing  Between  Outlets  in  Feet 


40  42 


FIG.  15. — Curves  for  selecting  type  of  reflector. 


units  until  it  intercepts  the  horizontal  line  marked 
"mounting  height,'7  and  use  the  shade  which  is  shown 
by  the  diagonal  line  to  be  nearest  the  point  thus  located. 


CHAPTER  VIII 
GENERAL  DATA 

Such  data  as  have  been  found  necessary  for  the  esti- 
mating and  laying  out  of  both  large  and  small  interior 
and  underground  electrical  installation  is  included  in 
this  chapter.  Data  such  as  can  usually  be  obtained  from 
tables  in  the  National  Electric  Code  and  from  manu- 
facturers' literature  are,  in  general,  omitted. 

INTEKIOR  CONSTRUCTION 

Conduit,  Elbows  and  Couplings. — Dimensions  referring 
to  this  material  are  omitted  as  the  same  can  be  obtained 
in  the  conduit  manufacturers'  catalogues. 

Wire. — The  diameters,  weights  and  resistances  for 
different  sizes  of  wire  can  likewise  be  obtained  in  the 
wire  manufacturers'  catalogues. 

TABLE  XLI. — OUTSIDE   DIAMETERS  OF  BUSHINGS  AND  LOCKNUTS 


Size,  in. 

Outside 
diameter  of 
bushings,  in. 

Outside 
diameter  of 
locknuts,  in. 

Thickness 
of  bushings, 
in. 

Thickness 
of  locknuts, 
in. 

H 

1 

1H 

Ke 

H 

H 

1K6 

IKe 

% 

>^ 

i 

Ifc 

w 

H 

^2 

IK 

1% 

2Ke 

He 

Ke 

1H 

2H 

2^6 

« 

KG 

2 

2^ 

3>^ 

% 

%6 

2y2 

3^ 

3% 

M 

KG 

3 

4 

4% 

% 

KG 

3>i 

4Ke 

5M 

1 

KG 

4 

5 

5% 

1 

KG 

74 


GENERAL  DATA 


75 


Locknuts  and  Bushings. — It  is  usually  necessary  to 
know  the  outside  diameter  of  locknuts  and  bushings  the 
diameters  of  which  establish  the  spacing  distances  of 
conduits  entering  junction  boxes,  etc. 

Panelboards. — The  approximate  sizes  of  panelboards 
are  included  as  such  sizes  very  often  determine  their 
location. 

TABLE  .XLII. — APPROXIMATE  SIZES  OF  PANELBOARDS1 


Number  of 
circuits 

Two-wire   mains,   two-wire  branches, 
dimensions,  inches 

Three-wire  mains,  two- 
wire  branches,  dimensions, 
inches,  110  volts 

110  volts 

220  volts 

2 

5.75  X  12 

7  X  12 

5.75  X  13.5 

4 

8.00  X  12 

10  X  12 

8.00  X  13.5 

6 

10.25  X  12 

14  X  12 

10.25  X  13.5 

8 

12.50  X  12 

17  X  12 

12.50  X  13.5 

10 

14.75  X  12 

21  X  12 

14.75  X  13.5 

12 

17.00  X  12 

24  X  12 

17.00  X  13.5 

14 

19.25  X  12 

27  X  12 

19.25  X  13.5 

16 

21.50  X  12 

30  X  12 

21.50  X  13.5 

18 

23.75.  X  12 

34  X  12 

23.75  X  13.5 

20 

26.00  X  12 

37  X  12 

26.00  X  13.5 

22 

28.25  X  12 

40  X  12 

28.25  X  13.5 

24 

20.50  X  12 

43  X  12 

30.50  X  13.5 

26 

32.75  X  12 

47  X  12 

32.75  X  13.5 

28 

35.00  X  12 

50  X  12 

35.00  X  13.5 

30 

37.25  X  12 

53  X  12 

37.25  X  13.5 

1  For  panels  where  N.E.C.  inclosed  fuses  of  30  amp.  and  under  are 
employed.  No  switches  are  assumed  to  be  used  on  branch  buses,  and 
the  main  buses  are  assumed  to  be  without  switches  or  fuses. 


76 


THE  ELECTRICAL  CONTRACTOR 


TABLE  XLIII. — APPROXIMATE  SIZES  OF  PANELBOARDS,  DIMENSIONS  IN 

INCHES1 


Number  of 
circuits 

Two-wire  mains,  two-wire  branches 

Three-wire   mains,   two- 
wire  branches,  110  volts 

110  volts 

220  volts 

2 

7   X  22 

7  X  22 

7  X  22 

4 

11  X  22 

11  X  22 

11  X  22 

6 

15  X  22 

15  X  22 

15  X  22 

8 

17  X  22 

'   20  X  22 

17  X22 

10 

20  X  22 

23  X  22 

20  X  22 

12 

23  X  22 

27  X  23 

23  X  22 

14 

27  X  23 

32  X  23 

27  X  23 

16 

29  X  23 

35  X  23 

29  X  23 

18 

32  X  23 

39  X  23 

32  X  23 

20 

35  X  23 

44  X  24 

35  X  23 

22 

39  X  23 

48  X  24 

39  X  23 

24 

41  X  24 

52  X  24 

41  X  24 

26 

44  X  24 

56  X  24 

44  X  24 

28 

48  X  24 

60  X  24 

48  X  24 

30 

52  X  24 

64  X  24 

52  X  24 

1  For  panels  where  fuses  and  switches  of  30  amp.  and  under  are  em- 
ployed for  branches  and  where  no  fuses  or  switches  are  provided  on  the 
main  buses. 

Knife  Switches. — 

TABLE  XLIV. — AVERAGE  OVERALL  DIMENSIONS  OF  N.E.C.  FUSED  AND 

FUSELESS  SWITCHES,  FRONT-CONNECTED l 


Size 

Double-pole, 
inches 

Three-pole, 
inches 

Four-pole, 
inches 

Five-pole, 
inches 

Fuseless  switches. 

H.  W.    D. 

H.  W.    D. 

H.  W.    D. 

H.  W.    D. 

30 

11     7  291s 

11   10  29fe 

11   12  29i6 

11   15  29ie 

60 

13     8  2% 

13  11  2% 

13  14  2% 

13  17  2^ 

100 

15     9  3H 

15  12  3K 

15  15  3}4 

15  19  3H 

200 

19  10  4^6 

19  13  4$i6 

19  17  4*1  6 

19  21  4*A6 

Fused  switches.  .  . 



H.  W.   D. 

H.  W.    D. 

H.  W.    D. 

H.  W.    D. 

30 

11     7  2iMe 

11   10  2i?l6 

11   12  2i?ie 

11  15  2iMa 

60 

13     8  3?6 

13  11  3H 

13  14  3H 

13  17  3H 

100 

17     9  4ft 

17  12  4ft 

17  15  4# 

17  19  4H 

200 

21   10  5 

21   13  5 

21   17  5 

21  21  5 

Data  furnished  by  the  Walker  Electric  Company,  Philadelphia. 


GENERAL  DATA 


77 


From  the  above  table  the  sizes  of  iron  boxes  for  knife 
switches  may  be  obtained. 

General. — Such  data  as  the  carrying  capacity  of  wires, 
the  number  of  wires  in  a  single  conduit,  the  sizes  of  such 
conduits  and  so  forth  can  be  found  in  Rules  18  and  28, 
1915  National  Electrical  Code,  as  issued  by  the  National 
Board  of  Fire  Underwriters. 

UNDERGROUND  CONSTRUCTION 

Excavation. — The  average  contractor  sublets  this  por- 
tion of  his  work,  the  cost  of  which  will  average  between 
50  cts.  and  $2  per  cubic  yard  depending  upon  the  soil. 

Concreting. — What  has  been  said  regarding  excava- 
tion applies  to  this  item  likewise,  the  cost  of  which  will 
average  between  $9  and  $15  per  cubic  yard.  For  con- 
tractors' estimates  on  their  own  concrete  work  the  fol- 
lowing table  giving  the  various  amounts  of  concrete, 
sand  and  stone  per  cubic  yard  of  rammed  concrete  in 
different  proportions,  will  be  found  useful. 

TABLE  XLV. — AMOUNTS  OF  CEMENT,  SAND  AND  STONE  REQUIRED  PER 
CUBIC  YARD  OF  RAMMED  CONCRETE 


Stone,  mixtures  1  in.  and  under 

Screened-out  amounts 

Concrete 

Sand 

Stone 

Concrete,  bbls. 

Sand,  cu.  yd. 

Stone,  cu.  yd. 

1 

2.0 

4 

1.46 

0.44 

0.89 

1 

2.5 

5 

1.19 

0.46 

0.91 

1 

3.0 

5 

1.11 

0.51 

0.85 

1 

3.0 

6 

1.01 

0.46 

0.92 

1 

3.0 

7 

0.91 

0.42 

0.97 

1 

4.0 

7 

0.83 

0.51 

0.99 

1 

4.0 

8 

0.77 

0.47 

0.93 

Brick  Work  in  Manholes. — What  has  been  said  regard- 
ing the  above  items  applies  to  this  item  likewise,  the 


78 


THE  ELECTRICAL  CONTRACTOR 


cost  of  which  will  average  between  75  cts.  and  $1.50  per 
cubic  foot. 

Vitrified  Ducts. — 

TABLE  XLVI. — OUTSIDE  DIMENSIONS  OF  VITRIFIED  DUCTS 


Type 

Bore,  round  or  square,  in. 

Outside  dimensions,  in. 

Single-way 

3U 

5  X    5  X  18 

Two-way  
Three-way  
Four-way 

3^ 

3^ 
3U 

4  X    9  X  24 
5  X  13  X  24 
9  X    9  X  24 

Six-way  

3U 

9  X  13  X  36 

Nine-way  
Nine-way  

3>i 

2 

13  X  13  X  36 
9  X    9  X  36 

Telephone  Cables, — The  usual  literature  of  wire  manu- 
factures does  not  give  the  outside  diameters  of  paper- 
covered  lead-encased  telephone  cables.  The  following 
table  applies  to  type  G  lead-covered  telephone  cables 
as  manufactured  by  the  Western  Electric  Company. 


TABLE  XL VII 


No.  of  pairs 

Outside  diameter,  in. 

No.  of  pairs 

Outside  diameter,  in. 

5 

H 

40 

2%2 

10 

KG 

50 

% 

15 

X 

60 

7A 

20 

%6 

75 

15/16 

25 

% 

100 

IKe 

30 

5/8 

120 

1^2 

35 

llAe 

150 

1%2 

200 

1% 

Electric  Light  and  Power  Cables. — The  usual  literature 
of  wire  manufactures  does  not  give  the  outside  diameters 
of  rubber-covered,  lead-encased  cables. 


GENERAL  DATA 


79 


Single  Conductor.— 

TABLE  XL VIII. — OUTSIDE  DIAMETERS  OF  CABLES  FOR  600  VOLTS 
PRESSURE  OR  LESS 


Size 

Thickness 
of  rubber,  in. 

Thickness 
of  lead,  in. 

Outside  diameter 

Solid,  in. 

Stranded,  in. 

14 

%4 

%4 

0.28 

0.30 

12 

%4 

%4 

0.30 

0.31 

10 

%4 

%4 

0.33 

0.34 

8 

%4 

%4 

0.35 

0.38 

6 

KG 

KG 

0.47 

0.47 

5 

KG 

KG 

0.50 

0.50 

4 

KG 

KG 

0.52 

0.52 

3 

KG 

KG 

0.53 

0.55 

2 

KG 

KG 

0.56 

0.58 

1 

%4 

KG 

0.63 

0.66 

0 

%4 

KG 

0.69 

00 

%4 

KG 

0.73 

000 

%4 

KG 

0.78 

0000 

%4 

KG 

0.84 

250  M 

3/32 

%4 

0.95 

300  M 

3/32 

%4 

1.02 

350  M 

3/B2 

%4 

1.08 

400  M 

3/32 

%4 

1.11 

450  M 

3/32 

^4 

1.19 

500  M 

3/32 

%4 

1.20 

550  M 

%4 

%2 

1.33 

600  M 

%4 

%2 

1.34 

650  M 

%4 

3/32 

1.38 

700  M 

%4 

%2 

1.41 

750  M 

%4 

%2 

1.44 

800  M 

%4 

%2 

1.47 

850  M 

%4 

%2 

1.50 

900  M 

%4 

%„ 

1.53 

950  M 

/  D  4- 

%4 

Xo  Z 

%2 

1.56 

1000  M 

%4 

%2 

1.59 

80 


THE  ELECTRICAL  CONTRACTOR 


Duplex  Conductor. — 

TABLE  XLIX. — OUTSIDE  DIAMETERS  OF  CABLES  FOR  600  VOLTS 
PRESSURE  OR  LESS 


Size 

Thickness  of 
rubber,  in. 

Thickness  of 
lead,  in. 

Outside  diameter, 
stranded,  in. 

14 

%4 

H4 

0.30  X  0.50 

12 

X* 

H4 

0.31  X  0.53 

10 

H4 

H* 

0.34  X  0.59 

8 

%4 

KG 

0.41  X  0.69 

6 

KG 

KG 

0.47  X  0.81 

5 

KG 

KG 

0.50  X  0.88 

4 

KG 

KG 

0.52  X  0.91 

3 

KG 

KG 

0'.55  X0.97 

2 

KG 

H4 

0.61  X  1.06 

1 

W4 

H4 

0.69  X  1.22 

0 

H4 

%4 

0.72  X  1.28 

00 

«4 

H4 

0.77  X  1-.38 

000 

H4 

%4 

0.81  X  1.47 

0000 

H4 

^4 

0.88X1.59 

250  M 

%i 

Ha 

0.95  X  1.64 

300  M 

3/32 

Hi 

1.02  X  1.88 

350  M 

3/32 

Ha 

1.08  X  2.00 

400  M 

3/32 

%2 

1.11  X  2.06 

450  M 

3/32 

.H2 

1.19  X  2.22 

500  M 

3/32 

H? 

1  .  20  X  2  .  24 

Triplex  Conductor. — 


Size 

Thickness  of 
rubber,  in. 

Thickness  of 
lead,  in. 

Outside  diameter 
stranded,  in. 

14 

H4 

KG 

0.59 

12 

%4 

KG 

0.63 

10 

%4 

KG 

0.70 

8 

%4 

KG 

0.77 

6 

Ke 

%4 

0.94 

5 

KG 

^4 

1.00 

4 

KG 

^4 

1.03 

3 

KG 

%4, 

1.09 

2 

KG 

Hi 

1.13 

1 

%4 

*/32 

1.19 

0 

%4 

H2 

1.28 

00 

%4 

H2 

1.38 

000 

%4 

%2 

1.50 

0000 

%4 

H2 

1.64 

INDEX 


AMPERES  PER  H.  P.  FOR  A.-C.  MOTORS 57 

ANNUNCIATOR  SYSTEMS,  COST  OF.   ..." 22 

B 

BELL  SYSTEMS,  COST  OF 22 

Bookkeeping 7-13 

Bills  and  billing 9,  11,  13 

Contract  ledger 7,  11,  17,  26 

Main  ledger 11 

Pay-roll  distribution 12,  13 

Order  cards  for  jobs 7,  8 

Order  cards  for  workman 8,  9 

Requisition  sheet 9-11 

Transferring  materials  on  jobs 9,11 

BUSHINGS,  DIMENSIONS  OF 74 


Cables. 

Cost  of  connecting  at  dynamo  and  switchboard 30 

Cost  of  pulling  and  splicing 39,  40 

Dimension  of  single-conductor  electric 79 

Dimension  of  double-conductor  electric 80 

Dimension  of  three-conductor  electric 80 

Dimension  of  telephone 78 

Candle  Power. 

Curves  of 64,  65 

Definition  of 62,  63 

Concreting. 

Cost  of 77 

Various  proportions  used  in 77 

Conduit. 

Cost  of  laying  rigid 38 

Cost  of  running  rigid 31 

Cost  of  running  flexible 31 

Construction  Department. 

Method  of  checking  weekly  costs 26-28 

81 


82  INDEX 

Requisition  sheets 9,10 

Special  receipt  sheets 9,11 

Stockroom 9,11,13 

Sup't 9,26,28 

Time  sheet 25 

Workman's  order  card 8,  9 

Costs 14-40 

Curves  of 15-17 

Items  of 14 

Method  for  obtaining  approximate 15-18 

Method  for  obtaining  unit 23-29 

Pay-roll  clerk's  sheet  of  unit 23 

Tables  of  approximate 18-22 

Tables  of  unit 29-40 

Time  sheet  lor  ascertaining  unit 25 

Weekly  sheets  of  unit 26,  27 

CROSS-ARMS,  COST  OF  ERECTING 37 

CURVES,  METHOD  OF  PREPARING 15-17 

D 

Ducts. 

Cost  of  laying 38 

Dimension  of 78 

DOUBLE  NEUTRAL  MAINS 49 

Dynomas. 

Cost  of 19 

Cost  of  connecting  cables 20,  30 

Cost  of  erecting  belted 29 

Cost  of  foundations  for  belted 29 

E 

ENGINEERING  DEFT.,  WORK  OF 9 

ENGINES,  COST  OF 18 

Estimates 41-45 

Detail  of  branches 42 

Detail  of  mains 43 

Interior  construction 41-42 

Logical  arrangement 41,  42,  44,  45 

Overhead  construction 44,  45 

Underground  construction 44 

EXCAVATING,  COST  OF 77 

Expenses  (Manufacture  or  Overhead} 1-6 

Items  of 3,  4 

Meaning  and  nature  of 2,  3 


INDEX  83 

Method  of  applying 5,  6 

Method  of  computing 4,  5 

National  electrical  contractors  association,  data  of 3 


FAN  OUTLET,  COST  OF  INSTALLING 21 

FIRE  ALARM  SYSTEMS,  COST  OF  INSTALLING 22 

FIXTURE  SUPPORTS,  COST  OF  INSTALLING 34 

FOOT  CANDLES,  DEFINITION  OF 63 

FOOT  CANDLES,  TABLE  OF 71 

FLUX  OF  LIGHT  METHOD 70-72 

G 

GLOBES,  ABSORPTION  OF  LIGHT  BY 69 

H 

HEATER  OUTLET,  COST  OF  INSTALLING 21 

HENRY'S  METHOD  OF  CALCULATING 58,  59 


Illumination 62-73 

Absorption  of  light  by  globes 69 

Calculating  size  of  units 68-71 

Candle-power,  definition  of 62,  63 

Candle-power,  curves 64,  65 

Desirable  size  of  squares  for  spacing 69 

Effect  of  reflection  from  walls 67,  68 

Foot-candles 63,  71 

Flux  of  light  method 70-72 

Indirect  lighting-watts  per  foot-candle 72 

Intensity  of  illumination 63-66,  71 

Lumens,  definition  of 70 

Lumens,  table  of  effective 71 

Reflectors 72,  73 

IMPEDANCE 59 

INDUCTANCE 53-59 

IRON  OUTLET,  COST  OF  INSTALLING 21 

J 

JOBS,  TRANSFERRING  MATERIALS  ON 9,  11 


84  INDEX 

K 

Knob-and-tube  Work. 

Cost  per  foot  for  concealed 35 

Cost  per  foot  for  exposed 36 

L 

LABOR,  VARIATIONS  IN  COST  OF 24,  28 

LIGHT  OUTLETS,  COST  OP  INSTALLING 21 

LOCKNUTS,  DIMENSION  OP 74 

LOSSES — A.-C.  circuits 53-61 

LOSSES — D.-C.  circuits 46-52 

LOSSES — at  contacts 50 

LUMEN,  DEFINITION  OF 70 

LUMEN,  TABLE  OF  EFFECTIVE 71 

M 

MANHOLES,  COST  OF  . 77,  78 

MOLDING  WORK,  COST  OF 36 

Motors. 

Cost  of 20 

Cost  of  installing  and  connecting 33 

Cost  of  installing  and  connecting  control  apparatus    ....  34 

Cost  of  wiring  and  connecting 21 

Current  consumption  of  A.-C 57 

MULTIPLYING  FACTORS  FOR  A.-C.  CIRCUITS 56 

O 

OHM'S  LAW 47 

ORDER  CARDS — JOB 7,  8 

ORDER  CARDS — WORKMAN 8,  9,  10 

OUTLETS,  COST  OF  WIRING  VARIOUS 21,  22 

Outlet  Boxes. 

Cost  of  installing  light 34 

Cost  of  installing  switch 34 

Cost  of  installing  receptacle  (floor) 34 

Cost  of  installing  receptacle  (wall) 34 

P 

Panel  Boards. 

Cost  of  installing 33 

Dimension  of .' 75,[76 

PAY-ROLL,  DISTRIBUTION  SHEET  FOR 


INDEX  85 

POLE  LINE  CONSTRUCTION 44,  45 

Poles 37 

Cost  of  digging  holes  for 37 

Cost  of  erecting  (iron) 37 

Cost  of  erecting  (wood) 37 

Cost  of  erecting  cross-arms  on 37 

Cost  of  guying 37 

Cost  of  shaving 37 

Cost  of  stepping 37 

Profit 1-6 

Meaning  and  nature  of 1,2,5,6 

Method  of  applying 5,  6 

National  Electrical  Contractors  Association,  data  of  ....       3 

Power-factor. 

Definition  of 53,  54 

Table  of  averages 54 

R 

REACTANCE 58,  59 

RECEIPTS — SPECIAL 9,  11 

Receptacles. 

Cost  of  installing  and  connecting 33 

Cost  of  installing  boxes  for 34 

Cost  per  outlet  for  floor 21 

Cost  per  outlet  for  wall 21 

REFLECTORS,  CURVES  OP  PROPER 72,  73 

REQUISITION  SHEETS 9,  10 

Resistance. 

Method  of  approximating 48 

Of  1/0  wire 48 

Of  a  circuit  carrying  a  given  current 51 

S 

SELF-INDUCTION 58 

SHOP  OR  REAL  COST 2 

SIGNAL  SYSTEMS,  COST  OF 22 

SKIN  EFFECT 53 

STOCK  ROOM 11 

Switches — (Push  button). 

Cost  per  outlet 21 

Cost  of  installing  and  connecting 33 

Cost  of  installing  boxes  for 34 

SWITCHES — (KNIFE),  DIMENSION  OF 76 


86  INDEX 

Switchboards. 

Cost  of 19 

Cost  of  connecting  cables  at 20,  30 

Cost  of  erecting 30 

T 

TELEPHONE  SYSTEMS,  COST  OF 22 

THREE-WIRE  BALANCE  SYSTEM 48,  49 

TIME  CLOCK  SYSTEMS,  COST  OF 22 

TIME  SHEETS 25 

TIME  STAMP  SYSTEMS,  COST  OF 22 

U 

UNDERGROUND  CONSTRUCTION 44 

V 

VACUUM  CONTROL  OUTLETS,  COST  OF 21 

VOLTAGE  LOSSES  ON  A.-C.  CIRCUITS 53-61 

VOLTAGE  LOSSES  oisi  D.-C.  CIRCUITS 46-52 

W 

WATCHMAN'S  CLOCK  SYSTEMS,  COST  OF 22 

Wire. 

Calculating  sizes  for  A.-C.  circuit 53-61 

Calculating  sizes  for  D.-C.  circuit 46-52 

Cost  per  ft.  fishing  conduits  and  pulling 32 

Cost  per  ft.  stringing 38 

Method  of  approximating  resistance  of 48 

Multiplying  factor  for  A.-C.  circuits 56 

Relative  sizes  of  for  D.-C.  and  A.-C.  .  55 


t 


3380 


153 


Engineering 
Library  - 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


